Interference relationship characterization in full duplex cable network environments

ABSTRACT

An example method for characterizing interference relationships in full duplex cable network environments is provided and includes generating a global interfered list for a plurality of cable modems in the cable network and for a plurality of frequency ranges, generating a global interfering list for the plurality of cable modems and for the plurality of frequency ranges, assigning respective downstream reception frequency ranges and upstream transmission frequency ranges for the plurality of cable modems based on the global interfered list and the global interfering list, and transmitting to the cable modems corresponding assignment information comprising the respective assigned downstream reception frequency ranges and upstream transmission frequency ranges.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. § 119(e)to U.S. Provisional Application Ser. No. 62/192,924 entitled “FULLDUPLEX OPERATION IN CABLE NETWORKS,” filed Jul. 15, 2015, which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates in general to the field of communications and,more particularly, to interference relationship characterization in fullduplex cable network environments.

BACKGROUND

Consumer appetite for bandwidth continues to grow exponentially in thecable network market. In some cable network architectures, includingremote physical layer (RPHY) with digital fiber, the coax fiber becomesthe bottleneck in throughput, stifling increase in bandwidth. Thetypical multi-system operator (MSO) is out of options currently, due tothe inherent technological limitations of existing cable networkcomponents. For example, the Shannon channel capacity limit (e.g., tightupper bound on rate at which information can be reliably transmittedover a communications channel) has practically been achieved already inexisting cable network architectures. There is consumer driven demand toextend the frequency spectrum beyond 1.2 GHz, but a conventionalextension would require extensive network upgrade. Upgrades in networkcomponents are limited by capital expenditure (CAPEX) budgetlimitations. All optics (fiber to the home (FTTH) have excessive CAPEX.In such scenarios, it may be desirable to offer new services with fulldownstream/upstream (DS/US) throughput (e.g., matching Gigabit-capablePassive Optical Networks (GPON) standard of 2.5 Gbits downstream/1 Gbitsupstream ratio) with limited capital expenditure for outside plantupgrade.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present disclosure andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIG. 1A is a simplified block diagram illustrating a communicationsystem comprising a full duplex network architecture in cable networkenvironments;

FIG. 1B is a simplified block diagram illustrating example details ofembodiments of the communication system;

FIG. 2 is a simplified block diagram illustrating other example detailsof embodiments of the communication system;

FIG. 3 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 4 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 5 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 6 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 7 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 8 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 9 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 10 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 11 is a simplified flow diagram illustrating example operationsthat may be associated with an embodiment of the communication system;

FIG. 12 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 13 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 14 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 15 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 16 is a simplified diagram illustrating example operations that maybe associated with an embodiment of the communication system;

FIG. 17 is a simplified flow diagram illustrating other exampleoperations that may be associated with an embodiment of thecommunication system;

FIG. 18 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 19 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 20 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 21 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 22 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 23A is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 23B is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 24 is a simplified diagram illustrating yet other exampleoperations that may be associated with an embodiment of thecommunication system;

FIG. 25 is a simplified diagram illustrating yet other exampleoperations that may be associated with an embodiment of thecommunication system;

FIG. 26 is a simplified block diagram illustrating yet other exampledetails of embodiments of the communication system;

FIG. 27 is a simplified flow diagram illustrating yet other exampleoperations that may be associated with an embodiment of thecommunication system;

FIG. 28 is a simplified flow diagram illustrating yet other exampleoperations that may be associated with an embodiment of thecommunication system;

FIG. 29 is a simplified flow diagram illustrating yet other exampleoperations that may be associated with an embodiment of thecommunication system;

FIG. 30A is a simplified diagram illustrating yet other example detailsof embodiments of the communication system;

FIG. 30B is a simplified diagram illustrating yet other example detailsof embodiments of the communication system; and

FIG. 30C is a simplified diagram illustrating yet other example detailsof embodiments of the communication system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

An example method for characterizing interference relationships in fullduplex cable network environments is provided and includes generating aglobal interfered list for a plurality of cable modems in the cablenetwork and for a plurality of frequency ranges, generating a globalinterfering list for the plurality of cable modems and for the pluralityof frequency ranges, assigning respective downstream reception frequencyranges and upstream transmission frequency ranges for the plurality ofcable modems based on the global interfered list and the globalinterfering list, and transmitting to the cable modems correspondingassignment information comprising the respective assigned downstreamreception frequency ranges and upstream transmission frequency ranges.

Example Embodiments

Turning to FIG. 1A, FIG. 1A is a simplified block diagram illustrating acommunication system 10 enabling full duplex network communication incable network environments in accordance with one example embodiment.FIG. 1 illustrates a cable network 12 (indicated generally by an arrow)facilitating full duplex communication between a cable modem terminationsystem (CMTS) 14 and one or more cable modems (CMs) 16. Network 12includes transceivers 18, amplifiers 20, and taps and splitters 22. CMTS14 includes an intelligent media access control (MAC) scheduler 26 thatenables a two-dimensional transmission-reception (T-R) coordination forinterference avoidance, along with a processor 27 and a memory element28 that facilitate executing instructions comprised in MAC scheduler 26.In various embodiments, cable modems 16 may be grouped into variousinterference groups 30 to enable full duplex communication with littleto no interference. Groups 30 may comprise radio frequency (RF) isolatedgroups that allow frequency re-use through intelligent MAC scheduling.

Transceivers 18 enable full band communication for both upstream anddownstream network traffic and implement dynamic interferencecancellation, also referred to herein as adaptive interferencecancellation (AIC). Note that as used herein, the term “upstream” refersto a communication direction from cable modems 16 towards CMTS 14; theterm “downstream” refers to a communication direction from CMTS 14towards cable modems 16. Amplifiers 20 enable full band communicationfor both upstream and downstream network traffic, and implement AIC withringing (e.g., echo) suppression. Taps and splitters 22 may enable fullband communication for downstream and upstream traffic.

Each of cable modems 16 supports full band communication, but operatesin simplex mode for upstream or downstream transmission. For example,each of cable modems 16 may be assigned non-overlapping frequency bandsfor upstream and downstream communication, yet the same set of carrierscan be used for the downstream and upstream communication, yielding adoubling of throughput compared to currently existing non-full duplexsystems. Communication system 10 can enable higher bandwidth (e.g.,bandwidth is the maximum amount of data that can travel through acommunication channel) and throughput (e.g., throughput refers to thequantity of data that actually does travel through the communicationchannel successfully) through full-duplex communication.

To explain generally, bandwidth limitations are solved in somecommunication networks through duplex communication. In a general sense,duplex communication is bidirectional, allowing both end nodes of acommunication channel to send and receive data simultaneously and one ata time. Both end nodes have the ability to operate as sender andreceiver at the same time, or take turns sending or receiving data.Duplex-based systems typically have dual communication channels thatprovide separate medium (e.g., paths) for upstream (US) (e.g., uplink,outgoing, transmitting) and downstream (DS) (e.g., downlink, incoming,receiving) communication. In full duplex mode, the node sends andreceives signals simultaneously on the same frequency range.

Examples of communication techniques include frequency divisionduplexing (FDD) and time division duplexing (TDD). In FDD, separatefrequency bands (e.g., carrier frequencies) are used at the transmitterand receiver. Because FDD uses different frequency bands for upstreamand downstream operations, the upstream and downstream communication donot interfere with each other. Examples of FDD systems include thefollowing: asymmetric digital subscriber line (ADSL) andvery-high-bitrate digital subscriber line (VDSL); cellular systems,including UMTS/WCDMA Frequency Division Duplexing mode and the CDMA2000system; IEEE 802.16 WiMax Frequency Division Duplexing mode.

In TDD, the upstream communication is separated from the downstreamcommunication by allocation of different time slots in the samefrequency range. For example, users, such as cable modems, are allocatedtime slots for upstream transmission and downstream reception. TDDallows asymmetric flow for upstream and downstream data transmission.TDD is advantageous in cases where upstream and downstream data ratesare asymmetric. The capacities of downstream communication links andupstream communication links are altered in favor of one direction overanother by providing greater time allocation through time slots todownstream reception intervals than to upstream transmission intervals.

Full duplex communication mechanisms that are not FDD or TDD have notbeen used in cable networks, because the inherent network architectureand communication protocols do not support such communicationmechanisms. For example, cable was first introduced in the United Statesin the late 1950s. For the next 30 years, nearly every mile of buriedcable was half duplex; thus, the network was capable of broadbandtransmission in the downstream direction, from the head end to thesubscriber, but not in the upstream direction—communication from thesubscriber back to the head end was possible only via a telephone line.In recent years, cable operators have been investing heavily to upgradetheir buried cables from half to full duplex as a necessary first stepto capitalize on the demand for integrated data and voice services.However, upstream transmissions continue to be slower than downstreamreceptions (typically 1.5 to 3 Mbps downstream and 500 Kbps to 2.5 Mbpsupstream).

Nevertheless, with a properly configured cable network architecture,such as cable network 12 of communication system 10, full duplexcommunication can drastically expand available upstream spectrum (e.g.,estimated 5 to 10 times upstream capacity increase). Full duplexcommunication can provide near symmetric downstream and upstreamthroughput. System capacities (e.g., bandwidth) can improve with fullduplex communication. Moreover, full duplex communication may betechnology-agnostic and/or standards/agnostic.

However, implementing full duplex in existing cable networks meet withcertain challenges. For example, a large transmitted signal coupled backto the receiver due to reflection (e.g., self-interference from thetransmit pathway into the receive pathway within one and sametransceiver) at any of the network components, including CMTS 14, cablemodems 16, transceivers 18, amplifiers 20 and taps and splitters 22 cankill the received signal at the receiver. Moreover, upstream transmitsignal from one of cable modems 16 may leak into the downstream pathwayof another of cable modems 16, causing interference. Unlikeself-interference, such inter-CM interference cannot be removed withmere echo cancellation techniques because the upstream transmit signalis unknown in the downstream pathway.

Embodiments of communication system 10 can resolve such issues byenabling full duplex communication using appropriately configuredcomponents and spectrum sharing techniques. Full duplex communicationcan be successfully implemented by suppressing (e.g., eliminating)transmitted signals that are coupled back to the receiver (e.g., as anecho, as an upstream signal leaking into the downstream pathway and viceversa, etc.). Sufficient transmitted signal cancellation and/orelimination can be achieved by leveraging (among other parameters) stateof art devices and digital signal processing technologies, high speedand high performance (e.g., high resolution) analog to digitalconverters (ADC), powerful devices with more signal processingcapability, an AIC scheme, and advanced MAC scheduling for spectrumsharing. In various embodiments, the AIC scheme suppresses at a receiver(of transceiver 18 or amplifier 20 appropriately) a signal transmittedby a transmitter (of transceiver 18 or amplifier 20 appropriately).Further, in addition to the AIC scheme, full band amplifier 20implements a ringing suppression scheme implementing echo cancellation.

According to embodiments of communication system 10, MAC scheduler 26implements a two-dimensional transmission-reception (T-R) coordinationscheme among cable modems 16 in cable network 12. According to the T-Rcoordination scheme, cable modems 16 are categorized into interferencegroups 30, such that no cable modem of any one interference grouptransmits upstream in a frequency range simultaneously as another cablemodem in the same interference group receives downstream in thefrequency range, facilitating full duplex communication in cable network12 across the frequency range. Cable modems 16 operate in simplex mode,while supporting full band operation for downstream reception andupstream transmission. Note that cable modems 16 in differentinterference groups 30 transmit upstream and receive downstreamsimultaneously in the frequency range. In various embodiments, CMTS 14receives and transmits network traffic across the entire frequencyrange, facilitating full duplex communication in cable network 12. Insome embodiments, cable modems 16 are classified into interferencegroups 30 through a ranging process.

In some embodiments, MAC scheduler 26 implements the T-R coordinationcentrally in cable network 12. To explain in further detail, theavailable frequency spectrum of communication system 10 is divided intofrequency resource blocks, comprising a band of adjacent frequencies(e.g., contiguous sub-carriers). OFDM symbols in time space are groupedinto the resource blocks in frequency space. According to the centrallyimplemented T-R coordination scheme, MAC scheduler 26 partitionsresource blocks available to any one interference group into at least afirst portion and a second portion; the first portion is reserved forupstream transmission, and the second portion is reserved for downstreamreception, such that the first portion and the second portion do notoverlap in time and frequency for any cable modem in the interferencegroup. In other embodiments, MAC scheduler 26 implements the T-Rcoordination in a distributed manner in cable network 12. According tothe distributed T-R coordination scheme, cable modems 16 managescheduling upstream transmission and downstream reception in any oneinterference group. MAC scheduler 26 transmits a downstream transmissionmap ahead of downstream transmission to cable modems 16, and cablemodems 16 schedule respective upstream transmission according to thedownstream map.

In various embodiments, a cable network operator may upgrade an existingcable network operating in simplex mode to a full duplex mode by addingappropriate components supporting full duplex communication. Forexample, the cable network operator may implement a method for fullduplex communication in cable network 12 by operating MAC scheduler 26implementing the above-described two-dimensional T-R coordination schemeamong cable modems 16, operating full band transceiver 18 implementingthe AIC scheme, and operating full band amplifier 20 implementing theAIC scheme and the ringing suppression scheme implementing echocancellation. The cable network operator may add to cable network 12 oneor more taps and splitters 22 that support full band communication incable network 12.

Moreover, capital expenditure for upgrading to full duplex communicationmay be reduced by reusing certain components. Turning to FIG. 1B, FIG.1B shows a simplified diagram illustrating network components of network12 that may be replaced or added in existing cable networks to enablefull duplex communication. Note that in some embodiments, such as N+marchitecture with m=0 (e.g., N stands for number of nodes, m stands fornumber of amplifiers after each node), amplifiers 20 are not used atall. In an example embodiment, a majority (e.g., 97%) of taps andsplitters 22 can be re-used for full duplex operation. This may bebecause standard tap and splitter combiner can operate in full band(e.g., 5-1000 MHz) for both upstream and downstream, supportingfull-duplex communication in the supported frequency band. Only aminority (e.g., 3%) of taps and splitters 22 that do not support fullband downstream and upstream may have to be replaced for full duplexcommunication. Likewise, because cable modems 16 are not operating infull duplex mode singly, they may be reused if they support the fullband (e.g., they include capability to perform FDD with full agility forupstream and downstream frequencies). Components in network 12 thatinclude diplexers (such as transceivers 18 and amplifiers 20) may haveto be replaced entirely to support full duplex communication.

In various embodiments, intelligent MAC scheduling may be used to avoidinterference among neighboring cable modems 16. Intelligent MACscheduling can include: (i) ranging (e.g., measuring and/or monitoringinterference among cable modems 16, for example, by establishinginterference groups 30), and (ii) T-R coordination (e.g., transmissionsand receptions are coordinated through a centric or distributedscheduler to avoid interference among cable modems 16). In someembodiments, the T-R coordination implements a two dimensional(frequency and time) interference avoidance scheme.

Ranging facilitates assigning cable modems 16 to one or moreinterference groups 30. In some embodiments, during ranging, each ofcable modems 16 transmits an interference pattern upstream. For example,the interference pattern could comprise a single tone at one or morefrequencies. Other cable modems 16 attempt to receive the interferencepattern on their downstream reception frequencies. Different frequenciesand/or marked tones for the interference pattern may facilitate manycable modems 16 using the same ranging frequency interval. In somecases, one cable modem may interfere with another, which interferes witha third cable modem, yet the third cable modem may not interfere withthe first cable modem. For example, there may be cases in which CM₁interferes with CM₂, which interferes with CM₃, but CM₃ does notinterfere with CM₁, leading to overlapping interference groups 30. Inone example embodiment, such overlapping groups may be lumped into oneoverarching group, with sub-groups therein.

In some embodiments, one of cable modems 16 may be scheduled to transmiton a specific frequency in a maintenance time window, and other cablemodems 16 report their downstream modulation error ratio (MER) orinterference level on that frequency to MAC scheduler 26 (or CMTS 14, orother appropriate report receiving module in cable network 12 ). Basedon the reported downstream MER or interference level (as the case maybe), a determination may be made as to which cable modems 16 areinterfered by the transmitting one of cable modems 16. The interferedcable modems 16 are associated with the transmitting one of cable modems16 on that frequency in a particular one of interference groups 30. Theprocess may be repeated for various frequencies and cable modems 16.Interference groups 30 may not be updated often. Updating interferencegroups 30 comprises informing cable modems 16 categorized in respectiveinterference groups 30 as to their membership. Membership of cablemodems 16 may change due to various environmental conditions, networkload balancing, bandwidth usage by particular CMs, and other factors. Insome embodiments, interference groups 30 may be updated when there arechanges to Hybrid fiber-coaxial (HFC); in other embodiments,interference groups 30 may be updated after a predetermined timeinterval (e.g., 24 hours).

In some embodiments, intelligent MAC scheduler 26 implements staticfrequency planning for T-R coordination. Spectrum sharing may beimplemented through dynamic transmission coordination to avoidinterferences. To explain interferences, consider upstream transmissionfrom CM₁. The upstream transmission from CM₁ may be coupled into CM₂ ata common tap-splitter 22 with limited isolation and cause interferencewith downstream reception at CM₂. The interference from CM₁ cannot becancelled out at CM₂ as CM₂ does not have any reference signal from CM₁(e.g., CM₂ cannot determine whether downstream reception at CM₂ is fromCMTS 14 or from CM₁).

To reduce interferences at cable modems 16, a CM frequency planningscheme is implemented in various embodiments. The frequency spectrumused in cable network 12 is divided into multiple frequency ranges thatalign with channel boundaries. For each one of cable modems 16 and eachfrequency range, those cable modems 16 are identified whose upstreamtransmissions interfere with downstream reception of that specific oneof cable modems 16, and those cable modems 16 whose downstreamreceptions are interfered by upstream transmissions of that specific oneof cable modems 16, if they operate on that same frequency (as is thecase in full duplex communication). MAC scheduler 26 avoids assigningcable modems 16 to frequency ranges that cause interferences among them.

Full duplex communication affects operation of various components ofcable network 12, and the implications are different on differentcomponents. For example, the implications on CMTS 14 arise in the twoareas: (a) full duplex involves CMTS 14 supporting throughputs of fullband downstream traffic and upstream traffic (this is mainly a capacityspecification to support the throughput); and (b) frequency planning andintelligent MAC scheduling, including establishinginterfering/interfered lists according to algorithms described herein,executing frequency planning algorithms and determining frequencyassignments, and T-R coordination as appropriate. In some embodiments,such functions can be integrated into MAC scheduler 26 at CMTS 14.

In some embodiments, full duplex communication may involve a majorre-design of transceiver 18. Transceiver 18 may be reconfigured byreplacing its diplexer with a 2-way combiner-splitter and othermodifications. Transceiver 18 may be rewired to support full bandoperation for both downstream and upstream, and for high capacity tosupport the throughput of full band downstream and upstream. Transceiver18 may also be changed to implement AIC algorithms. Other functions tosupport full duplex include: measuring interferences among cable modems16 for frequency planning; and measuring cable modem downstream timingand upstream timing for supporting T-R coordination as appropriate.

Although cable modems 16 operate in FDD mode (e.g., downstream receptionand upstream transmission on different frequencies in any one cablemodem), cable modems 16 support full band FDD operation of bothdownstream and upstream. Full band FDD means downstream and upstreamfrequencies can be on any frequencies between 10 MHz to 1000 MHz (1.2GHz) although they do not overlap each other. This means that cablemodems 16 do not include any diplexer. In addition, cable modems 16 havefull frequency agility, good RF fidelity (e.g., with minimized guardband between downstream and upstream), and high capacity to support fullband throughput (e.g., 500 MHz DS and 500 MHz US).

Amplifier 20 may be subject to a major re-design to support full duplexcommunication. For example, amplifier 20 may be re-designed with nodiplexer, full band operation, and digitized input signal. Interferencecancellation blocks including ringing suppression may be added toexisting amplification functions. Amplifier 20 implementing a two-stepinterference cancellation scheme can provide over 50 dB interferencesuppression and push the interference below the noise floor. However,some signal integrity degradation may be inevitable. For example, if theinterference is suppressed to 6 dB below the system noise floor, theremay be 1 dB degradation to signal's ratio of signal-to-noise ratio (SNR)to modulation error ratio (MER) (SNR/MER). In some embodiments, themaximum number of the cascaded amplifiers (including trunk, bridge andextender) may be limited to 5 (N+5, max 5 dB degradation at the end ofthe line), for example, to minimize signal degradation.

The optical link in HFC may be changed to support full duplex operationby providing high capacity for both DS and US to support the highthroughput of coaxial network under full duplex. In a general sense,amplifiers in the coax network may be replaced. Devices with built-indiplexer (for example, reverse attenuator) in the coax network may bereplaced (3% of taps, according to Cisco CATV market). System gainre-engineering/re-balance may be suitable due to the extendedfrequencies. Some of the devices may be replaced (with betterport-to-port isolation) to enhance isolation among cable modems 16.Occasionally, the coax network may be re-architected to enhanceisolation among cable modems 16. For example, an amplifier may be addedright before a splitter to create isolated cable modem groups.

Full duplex could significantly increase cable access upstreamthroughput. An enabler for full duplex is interference cancellation andavoidance. Simulation results show that interference cancellation can beachieved through advanced digital signal processing algorithms. Fullduplex is perpendicular to (e.g., orthogonal to, independent of, etc.)cable access technologies and high layer architectures; thus, it canwork with any high level protocols and architectures. Full duplex can beused with existing access technology (CABU R-PHY shelf/node and CDBUCM), or as a candidate for next generation DOCSIS access technology.Full duplex is novel and substantial, and has business and technologyimpacts that may go beyond cable access (wireless, for example).

Turning to the infrastructure of communication system 10, the networktopology can include any number of cable modems, customer premisesequipment, servers, switches (including distributed virtual switches),routers, amplifiers, taps, splitters, combiners and other nodesinter-connected to form a large and complex network. Network 12represents a series of points or nodes of interconnected communicationpathways for receiving and transmitting packets and/or frames ofinformation that are delivered to communication system 10. A node may beany electronic device, computer, printer, hard disk drive, client,server, peer, service, application, or other object capable of sending,receiving, amplifying, splitting, or forwarding signals overcommunications channels in a network. Elements of FIG. 1 may be coupledto one another through one or more interfaces employing any suitableconnection (wired or wireless), which provides a viable pathway forelectronic communications. Additionally, any one or more of theseelements may be combined or removed from the architecture based onparticular configuration needs.

Cable network 12 offers a communicative interface between cable networkcomponents, and may include any local area network (LAN), wireless localarea network (WLAN), metropolitan area network (MAN), Intranet,Internet, Extranet, wide area network (WAN), virtual private network(VPN), or any other appropriate architecture or system that facilitatescommunications in a network environment. Network 12 may implement anysuitable communication protocol for transmitting and receiving datapackets within communication system 10. The architecture of the presentdisclosure may include a configuration capable of DOCSIS, TCP/IP, TDMA,and/or other communications for the electronic transmission or receptionof signals in a network. The architecture of the present disclosure mayalso operate in conjunction with any suitable protocol, whereappropriate and based on particular needs. In addition, gateways,routers, switches, and any other suitable nodes (physical or virtual)may be used to facilitate electronic communication between various nodesin the network.

In some embodiments, a communication link may represent any electroniclink supporting a network environment such as, for example, cable,Ethernet, wireless technologies (e.g., IEEE 802.11x), ATM, fiber optics,etc. or any suitable combination thereof. In other embodiments,communication links may represent a remote connection through anyappropriate medium (e.g., digital subscriber lines (DSL), coaxial fiber,telephone lines, T1 lines, T3 lines, wireless, satellite, fiber optics,cable, Ethernet, etc. or any combination thereof) and/or through anyadditional networks such as a wide area networks (e.g., the Internet).

Note that the numerical and letter designations assigned to the elementsof FIG. 1 do not connote any type of hierarchy; the designations arearbitrary and have been used for purposes of teaching only. Suchdesignations should not be construed in any way to limit theircapabilities, functionalities, or applications in the potentialenvironments that may benefit from the features of communication system10. It should be understood that communication system 10 shown in FIG. 1is simplified for ease of illustration.

In particular embodiments, CMTS 14 may comprise a hardware appliancewith appropriate ports, processors, memory elements, interfaces, andother electrical and electronic components that facilitate the functionsdescribed herein, including providing high speed data services, such ascable Internet or voice over Internet Protocol (e.g., in the form ofdigital, RF, or other suitable signals) to cable subscribers, such ascable modems 16. In various embodiments, CMTS 14 comprises a UniversalBroadband Router (uBR) with features that enable it to communicate witha Hybrid Fiber Coaxial (HFC) cable network via a suitable cable modemcard, which provides an interface between the uBR protocol controlinformation (PCI) bus and radio frequency (RF) signals on the DOCSIS HFCcable network.

In some embodiments, CMTS 14 may comprise a converged cable accessplatform (CCAP) core that transmits and receives digital signals in IPprotocols, coupled with one or more physical interface (PHY)transceiver(s), such as transceiver 18 that convert the digital IPsignals into RF signals, and vice versa. The PHY transceivers, such astransceiver 18, may be co-located with the CCAP core at a commonlocation, or may be located remote from the CCAP core and connected overa converged interconnect network (CIN). In some embodiments, CMTS 14 maycomprise a single CCAP core and a plurality of PHY transceivers, such astransceiver 18. CMTS 14 is connected (e.g., communicatively coupled, forexample, through wired or wireless communication channels) to cablemodems 16, transceiver 18, and amplifier 20 in cable network 12.

In some embodiments, intelligent MAC scheduler 26 may comprise ahardware device or software application or combination thereof executingwithin CMTS 14 to facilitate spectrum sharing by cable modems 16. Inother embodiments, intelligent MAC scheduler 26 may comprise a hardwaredevice or software application executing outside CMTS 14, for example,in a separate appliance (e.g., fiber coaxial unit (FCU) access node,etc.), server, or other network element and coupled to (e.g., connectedto, in communication with, etc.) CMTS 14 in cable network 12.

Transceivers 18 may comprise suitable hardware components and interfacesfor facilitating the operations described herein. In some embodiments,transceivers 18 may be embedded in or be part of another hardwarecomponent, such as a broadband processing engine comprising amotherboard, microprocessors and other hardware components. In someembodiments, transceivers 18 comprise downstream and upstream PHYmodules, deployed in a Coaxial Media Converter (CMC) that supports RFfunctions at the PHY layer. Transceivers 18 may comprise pluggablemodules (e.g., small form-factor pluggable (SFP)) that may be pluggedinto a network element chassis, or embedded modules that attach tocables directly. In addition to optical and electrical interfaces,transceivers 18 include a PHY chip, appropriate digital signalprocessors (DSPs) and application specific integrated circuits (ASICs)according to particular needs. In various embodiments, the DSPs intransceivers 18 may be adapted (e.g., programmed) to perform appropriateinterference cancellation as described herein to enable full duplexcommunication.

Amplifiers 20 comprise RF amplifiers suitable for use in cable network12. Amplifiers 20 are typically used at intervals in network 12 toovercome cable attenuation and passive losses of electrical signalscaused by various factors (e.g., splitting or tapping the coaxialcable). Amplifiers 20 may include trunk amplifiers, distributionamplifiers, line extenders, house amplifier and any other suitable typeof amplifier used in cable networks. According to various embodiments,substantially all amplifiers 20 are configured suitably as describedherein to facilitate full duplex communication.

Turning to FIG. 2, FIG. 2 is a simplified diagram illustrating exampledetails of frequency planning by MAC scheduler 26 according to anexample embodiment of communication system 10. Various frequency rangesused by cable modems 16 in any one of interference groups 30 may bedivided in time into resource blocks, such as upstream resource blocks32, downstream resource blocks 34 and guard time resource blocks 36. Ina general sense, the time and frequency employed to transmit an amountof data may be grouped as a resource block. In some embodiments, eachresource block may comprise 8 or 16 symbols in time, and 1 subcarrier infrequency. The frequency division aligns with channel boundaries in someembodiments. In other embodiments, the frequency division has finergranularities, such as corresponding to groups of subcarriers for DOCSIS3.1. The time division aligns with frame boundaries in some embodiments.In other embodiments, the time division aligns with mini-slotsboundaries. In various embodiments, upstream resource blocks 32 anddownstream resource blocks 34 in the relevant interference group do notsynchronize on the time division boundaries; there is no overlap betweenupstream transmission and downstream receptions in frequency-time spacewithin the same interference group.

In some embodiments, a centric scheduler algorithm may be used toachieve T-R coordination with the described resource allocation scheme.Other embodiments use a distributed scheduler algorithm for T-Rcoordination. With the centric scheduler algorithm, the resourcescheduling in time and frequency is done centrally, for example, withMAC scheduler 26 in CMTS 14. In the distributed scheduler algorithm, theupstream scheduling is done mainly by cable modems 16 through acontention scheme. CMTS 14 assists the upstream scheduling by policingresource usage by cable modems 16 to avoid the collision. In otherwords, it is a contention based upstream scheduling with collisionavoidance. The distributed scheduler algorithm is similar in some waysto the centric scheduler algorithm, in that the distributed algorithmdivides the available bandwidth into resource blocks, and follows therule of no overlapping of downstream resource blocks 34 and upstreamresource blocks 32 within any one of interference groups 30.

A simplex bi-directional signaling channel is established between CMTS14 and cable modems 16 to exchange scheduling information. CMTS 14broadcasts the downstream resource block allocation informationcomprising a downstream media access protocol (MAP) message to cablemodems 16 in the signaling channel ahead of the actual allocation time.Cable modems 16 listen to the downstream MAP in the signaling channel.Based on the downstream MAP, cable modems 16 sort out upstream resourceblocks 32 available for upstream transmission. In various embodiments, aspecific downstream MAP message may be applicable to (e.g., correspondwith) a particular one of interference groups 30. Based on queue depth(e.g., amount of data queued to be transmitted), cable modems 16 reserveupstream resource blocks 32 by sending a reservation notice to CMTS 14.CMTS 14 echoes the cable modems' reservations in a downstream signalingchannel with time stamps. Each of cable modems 16 receives an echo ofits own reservation and reservation of other cable modems 16, with timestamps. The specific one of cable modems 16 with the earliest time stampfor its reservation may seize upstream resource blocks 32 and starttransmitting.

The downstream and upstream scheduling are not independent of eachother. For a specific one of cable modems 16, MAC scheduler 26 mayschedule its upstream transmission in certain upstream resource blocks32; further, MAC scheduler 26 may ensure that other cable modems 16 fromthe same interference group receive their downstream receptions indownstream resource blocks 34 that do not overlap with scheduledupstream resource blocks 32 of the specific one of cable modems 16.Likewise, for the specific one of cable modems 16, MAC scheduler 26 mayschedule its downstream reception in certain downstream resource blocks34; further, MAC scheduler 26 may ensure that other cable modems 16 fromthe same interference group transmit upstream in upstream resourceblocks 32 that do not overlap with the scheduled downstream resourceblocks 34. Multicast and broadcast messages may be scheduled on specificresource blocks without upstream transmission from any cable modems 16.In the case of broadcast video, a block of downstream spectrum (e.g.,frequency range) may be allocated for broadcast video, and thecorresponding upstream spectrum may be idled to avoid interference tovideo at cable modems 16.

Turning to FIG. 3, FIG. 3 is a simplified diagram illustrating exampledetails of T-R coordination according to an embodiment of communicationsystem 10. Consider T-R coordination among two CMs, CM₁ and CM₂ in aparticular one of interference groups 30 in cable network 12. MACscheduler 26 may allocate resource blocks 38 to CM₁ and resource blocks40 to CM₂. Note that for ease of illustration, upstream resource blocksand downstream resource blocks comprised in resource blocks 38 and 40are not explicitly shown. MAC scheduler 26 will not schedule CM₂ totransmit upstream on the same frequency at the same time when CM₁ isreceiving downstream. In other words, CM₁ and CM₂ do not haveoverlapping resource blocks for upstream transmission or downstreamreception. Such pairwise relationship holds for any pair of cable modems16 in any one of interference groups 30.

Turning to FIG. 4, FIG. 4 is a simplified block diagram illustratingexample details of an embodiment of communication system 10. In someembodiments, MAC scheduler 26 may operate centrally in cable network 12,implementing T-R coordination centrally, for example, at CMTS 14. MACscheduler 26 categorizes cable modems 16 into interference groups 30,and schedules upstream transmissions and downstream receptions for cablemodems 16 in each interference group 30, such that no cable modem of anyone interference group transmits upstream in a frequency rangesimultaneously as another cable modem in the same interference groupreceives downstream in the frequency range. The scheduling can allowcable modems 16 in different interference groups 30 to transmit upstreamand receive downstream simultaneously in the frequency range. MACscheduler 26 generates scheduling information of the scheduling. Thescheduling information may be comprised in appropriate MAC controlmessages in some embodiments. MAC scheduler 26 transmits the schedulinginformation to cable modems 16.

In various embodiments, downstream reception time is interleaved in azig zag pattern such that downstream data spans multiple symbolsoverlapped with each other. In a general sense, “interleaving” refers tospreading data over some parameter; data spread over time is referred toas time interleaved data; data spread over frequency is referred to asfrequency interleaved data. For example, data comprised in one symbolbefore interleaving is spread across 32 symbols after interleaving. Notethat the term “symbol” has the general meaning familiar to persons withordinary skill in the art and refers to a time interval forcommunicating bits of data that are modulated onto carriers at certainfrequencies according to the modulation scheme used for thecommunication (e.g., in a single carrier modulation scheme, as higherdata rates are used, the duration of one symbol becomes smaller); datais coded into the frequency domain one symbol at a time. In other words,data is carried in communication channels in cable network 12 in unitsof symbols in the time domain and frequency sub-carriers in thefrequency domain.

Prior to interleaving, subsequent symbols containing downstream data arenot overlapped; after interleaving, the downstream data spans multiplesymbols and is effectively overlapped with itself. In an example, apacket of data that fits into one or two symbols occupies 32 symbolsafter interleaving. In various embodiments, upstream transmission timeis not interleaved. In various embodiments, downstream transmissionfrequency is interleaved across a downstream symbol spanning a frequencyrange of an orthogonal frequency division multiplex (OFDM) resourceblock (e.g., 192 MHz) (and not the entire frequency spectrum availablefor cable network 12). Upstream transmission frequency is interleavedacross an upstream symbol. The upstream symbol is aligned with thedownstream symbol.

To facilitate interleaving in the time and frequency domain,interference groups 30 may be further sorted into interference blocks(IBs) 42. Each interference block 42 comprises a plurality of symbolsincluding a symbol for guard time, with interleaving being implementedusing interference blocks 42. In some embodiments, cable modems 16 maybe sorted into interference groups 30 at initialization using a specialranging process. Interference groups 30 are sorted into interferenceblocks 42. Note that interference blocks 42 can comprise any suitable(e.g., convenient, appropriate) grouping of interference groups 30. Inan example embodiment, interference blocks 42 may be designated by smallletters a, b, c, d, for example, to distinguish them from DOCSIS 3.1profile designations of capital letters A, B, C, D. In an exampleembodiment, any one interference block 42 may equal 32 symbols(comprising the interleaved symbols) and one additional symbol for guardtime, totaling 33 symbols in all. The guard time symbol may not be adedicated symbol, but may be conveniently chosen based on the datapattern or other parameters as appropriate.

In some embodiments, a number (e.g., 100) of interference groups 30 maybe mapped to a relatively much smaller number (e.g., 4) of interferenceblocks 42. In other embodiments, a number of interference groups 30(e.g., 100) may be mapped to an equal or similar order of magnitudenumber of interference blocks 42 (e.g., 100 or 50). In the latterembodiments, each interference block 42 may serve as a guard time indownstream transmissions from CMTS 14 to cable modems 16. The upstreamtransmissions would ignore 3× interference block times (e.g., firstinterference block time during which it is supposed to receivedownstream data, and two other interference blocks on either side of thefirst interference block time). With dynamic assignment of interferencegroups 30 to interference blocks 42, each interference group 30 can get97% of the spectrum between downstream reception and upstreamtransmission. In a general sense, delay and timing differences withinany one of interference groups 30 can be accommodated with a one symbolguard time, whereas delay and timing differences between CMTS 14 andinterference groups 30 may be accommodated with additional guard time.

Turning to FIG. 5, FIG. 5 is a simplified block diagram illustratingexample details according to an embodiment of communication system 10.Consider an example transmission comprising four interference blocks 42.In other words, interference groups 30 are categorized into 4interference blocks 42 (e.g., 100 interference groups map to 4interference blocks), namely, a, b, c, and d. Without time interleaving,interference blocks a, b, c, d may be stacked one after the other in arepeating pattern. With time interleaving, interference blocks a, b, c,and d may overlap with each other in time according to the extent ofinterleaving. In some embodiments, time offset may also be implemented,for example, with the next set of interference blocks 42 being some timeapart from the previous set of interference blocks 42, for example, toaccount for time delays and other factors. Such time offset may includeguard times to account for delays among cable modems 16, between CMTS 14and cable modems 16, etc.

Turning to FIG. 6, FIG. 6 is a simplified block diagram illustratingexample details according to an embodiment of communication system 10.In non-full-duplex cable networks, a cyclic prefix (CP) is different forthe downstream symbol and the upstream symbol because they are atdifferent frequencies. However, with full duplex communication, thedownstream symbol and upstream symbol can be at the same frequency. Invarious embodiments, the CP is the same for a particular frequency,regardless of the direction (e.g., upstream or downstream) oftransmission, facilitating alignment of downstream and upstream symbolsper OFDM resource block. In some embodiments, the time-space alignmentof downstream symbols with upstream symbols can be representedfiguratively by trapezoids in the downstream lining up with rectanglesin the upstream direction. The “bottom” side of the trapezoid would bedifferent in length from the “top” side depending on the amount of timeinterleaving. In such a figurative representation, the top of thedownstream trapezoid would be zero interleaved and can be considered areference point.

Consider an example transmission comprising four interference blocks 42.In other words, interference groups 30 are categorized into 4interference blocks 42 (e.g., 100 interference groups map to 4interference blocks), namely, a, b, c, and d. In such exampleembodiments, if all interference blocks 42 are of equal bandwidth, theneach interference group 30 is only getting 25% of the frequencyspectrum.

Each interference block 42 is 33 symbols wide in this example. Assumethat interference blocks 42 allocated for downstream transmission arereferred to as downstream blocks 44 in pattern a-b-c-d-repeat;interference blocks 42 allocated for upstream transmission are referredto as upstream blocks 46 in pattern c-d-a-b-repeat. Downstream blocks 44could be lined up with the upstream blocks 46 with an offset of 2blocks. The gap between blocks a and c is the guard time (comprisingblocks b and d). The guard time is at least 32 symbols wide toaccommodate downstream frequency interleaving. An extra symbol isincluded to allow for time differences within an interference group fora total of 33 symbols.

Turning to FIG. 7, FIG. 7 is a simplified block diagram illustratingexample details according to an embodiment of communication system 10.In a general sense, when a time domain interleaving scheme is typicallyimplemented at the symbol level, different carriers of the OFDM symbolare delayed by different amounts. As the carrier allocation is alongfrequency, the interleaving in time will be effective for burstinterferences; the interferences will be spread across the symbols intime axis, into multiple forward error correction (FEC) blocks. In thecase where the burst interference covers many sub-carriers, theinterleaving depth is large enough to minimize the numbers of interferedsub-carriers for each FEC block. However, time interleaving introducesdelay, which equals the interleaving depth.

According to some embodiments, interleaving 50 takes advantage of themultiple FEC blocks along frequency at each symbol. Time interleaving 52is performed on the symbols, and frequency interleaving 54 is added totime interleaving 52, for example, to achieve better interleavingefficiency with minimized delay. Accordingly, symbols at each symboltime are re-arranged through a simple storage access scheme withoutintroducing any delay. With addition of frequency interleaving 54 totime interleaving 52, effective interleaving depth is a product offrequency interleaving depth and time interleaving depth. Interleaveddata is subjected to Inverse Fast Fourier Transform (IFFT) and sentacross a burst channel. At the receiver, the received data is subjectedto Fast Fourier Transform (FFT) and frequency de-interleaving 56,followed by time de-interleaving 58.

Turning to FIG. 8, FIG. 8 is a simplified block diagram illustratingexample details according to an embodiment of communication system 10.According to the embodiments interleaving 50, in which time interleaving52 is added to frequency interleaving 54, interferences fall intodifferent FEC blocks after de-interleaving even with shallowinterleaving depth along time, leading to enhanced interleavingperformance with a minimum delay.

Turning to FIG. 9, FIG. 9 is a simplified block diagram illustratingexample details of frequency interleaving 54 according to an embodimentof communication system 10. Consider a hypothetical example comprising amapping 60 between symbols 62 and sub-carriers 64. Twelve symbols 62 aremapped to corresponding twelve sub-carriers 64 in mapping 60. Accordingto frequency interleaving 54, sub-carriers 64 are arranged into twocolumns and are ordered in an ascending order along each of the columns(e.g., 1-6 in column 1 and 7-12 in column 2). Sub-carriers 64 arere-ordered by reading the rows of the two columns in an ascending order(e.g., bottom to top). The final order of sub-carriers 64 afterfrequency interleaving 54 is no longer in a purely ascending order.Final mapping 66 between symbols 62 and sub-carriers 64 is differentfrom mapping 60 before frequency interleaving 54.

Turning to FIG. 10, FIG. 10 is a simplified block diagram illustratingexample details of interleaving 50 according to an embodiment ofcommunication system 10. To explain further, consider an example with16384 sub-carriers (192 MHz, 12.5 kHz CS). The 16384 sub-carriers arearranged into 8 columns, each column having 2048 sub-carriers. With16200 bit-density parity-check (LDPC) and 256-Quadrature amplitudemodulation (QAM), each column has one FEC codeword (CW). At theinterleaving stage, mapping between symbols and sub-carrier is such away that the symbols are written along columns, and read out along rows.At the de-interleaving stage, symbols are written along rows, and readout along columns.

Turning to FIG. 11, FIG. 11 is a simplified flow diagram illustratingexample operations 70 according to an embodiment of communication system10. Operations 70 may be assumed to be executed at a specific one ofcable modems 16. In some embodiments, a distributed intelligentscheduling scheme is implemented by MAC scheduler 26 for T-Rcoordination, for example, to make the scheduling scheme more scalable.The distributed intelligent scheduling is enforced by cable modems 16and is not centrally enforced at CMTS 14. The distributed schedulingscheme keeps the downstream and upstream scheduling asynchronous witheach other.

In general, according to the distributed scheduling scheme, cable modems16 are divided into a large number of interference groups 30, eachhaving a relatively small number of cable modems 16. Interference groups30 are established with a ranging process. Downstream transmission in afrequency range from CMTS 14 to cable modems 16 is implemented in one ormore transmission units, such as FEC CW. Each FEC CW includes a grouplabel identifying the specific interference group that is receiving datafor that FEC CW, distinguishing the downstream transmission in thefrequency range to the interference group from downstream transmissionsto other interference group. In an example embodiment, the FEC CW grouplabel may be included in a FEC next codeword pointer field (NCP)according to DOCSIS 3.1 standards. At 72, the cable modem executingoperations 70 receive the FEC CW. At 74, it identifies the targetinterference group from the group label in the FEC CW. At 76, adetermination is made whether the target interference group is the sameas the local interference group to which the cable modem belongs. If thelocal interference group is not the target interference group, the FECCW (and subsequent downstream transmission) may be disregarded at 78.

If the local interference group is the target interference group, thecable modem determines the downstream reception time window at 80. Thegroup label in the FEC CW is several CW times in advance or in aseparate structure so that the cable modem in the target interferencegroup can anticipate receiving the downstream data ahead of actualreception, and schedule upstream transmission accordingly. At 82, thecable modem makes a determination whether it has scheduled any upstreamtransmission during the anticipated time window. According to variousembodiments, cable modems 16 in the target interference group receivingthe FEC CW are not allowed to transmit upstream. Because cable modems 16request bandwidth ahead of time of upstream transmission, some cablemodems 16 may have received a grant during the time window of downstreamtransmission. (CMTS 14 is not enforcing scheduling restrictions, andfreely issues grants.) Thus, the determination at 82 may includeidentifying any grants available for use during the anticipated timewindow.

If no upstream transmission is scheduled, at 84, the cable modemschedules upstream transmission outside the anticipated time window(e.g., prior to, or after, the anticipated time window). At 86, thecable modem associates minislots or symbols times in upstreamtransmissions with minislots or symbols in downstream receptions,aligning upstream and downstream symbols. On the other hand, if upstreamtransmission is scheduled, at 88, the cable modem suppresses upstreamtransmission during the anticipated time window, forfeiting the upstreamtransmission opportunity. At 90, the forfeiture can be managed byre-issuing requests to CMTS 14 with higher priority. In someembodiments, CMTS 14 may poll target cable modems to which it is sendingdownstream transmissions to check on suppressed transmissions.

In some embodiments, downstream bandwidth per cable modem being limited,downstream bandwidth per interference group can be rate-limited in ahierarchical manner to prevent upstream transmissions from being lockedout. Embodiments of communication system 10 may not require anydownstream and upstream calibration and alignment at CMTS 14. Long guardtimes may also be unnecessary, for example, due to large serving areasizes. The reference is local to the cable modems 16 that are closeenough to impact each other. In various embodiments, cable modems 16 are“warned” ahead of time of downstream transmission of data and cansuppress upstream transmission accordingly.

Each one of interference groups 30 becomes a simplex group in whichtransmission occurs in one direction at a time. Because the sizes (e.g.,memberships) of interference groups 30 are small and there are many ofthem, the overall effect in cable network 12 is full duplexcommunication. In various embodiments, any one cable modem has anaggregate bandwidth equal to one copy of the full spectrum. The overallinterference group on a node has an aggregate bandwidth equal to twotimes the spectrum.

In some embodiments that include the distributed intelligent scheduling,a first interference group predicts that a particular frequency range isnot going to be used for upstream transmission by a second interferencegroup and hijacks the frequency range for its own upstream transmission.Prediction may be based upon traffic to one or more cable modems in thesecond interference group, priorities of traffic or devices, back-uplist information from CMTS 14, set of contention REQ slots, or othersuitable parameters.

Turning to FIG. 12, FIG. 12 is a simplified block diagram showingexample details of MAC scheduler 26 according to embodiments ofcommunication system 10. MAC scheduler 26 includes a ranging scheduler100, a report receiver 102, a MER analyzer 104, a classifier 106, anaggregator 108, a frequency planner 110, and a group generator 112.Memory element 28 may store various data, including one or moreinterfered list 114, a global interfered list 116, one or moreinterfering list 118, and a global interfering list 120.

During frequency planning and grouping, MAC scheduler 26 may generate,for a particular one of cable modems 16 (say CM₁) in cable network 12,interfered list 114 associated with a frequency range. Interfered list114 comprises a first list of cable modems 16 whose downstream receptionin the frequency range is interfered by upstream transmissions of cablemodem CM₁ in the frequency range. Assume, merely for example purposes,that the first list of cable modems comprises cable modems CM₂ and CM₃.In other words, interfered list 114 for CM₁ comprises CM₂ and CM₃. MACscheduler 26 may repeat the interfered list generating process for othercable modems 16 (e.g., CM₁ . . . CM_(m)) in cable network 12. Forexample, interfered list 114 for CM₂ may comprise CM₂ and CM_(m);interfered list 114 for CM₃ may comprise CM₁ . . . CM_(m); etc.

The interfered list generating process is repeated for other frequencyranges in the frequency spectrum used in cable network 12. For example,the frequency spectrum may be divided into n frequency ranges (e.g.,F(1) to F(n)), and the interfered list generating process may berepeated for each one of the n frequency ranges, with separateinterfered lists 114 being generated for each frequency range and eachcable modem in cable network 12. Aggregator 108 may aggregate thegenerated interfered lists into global interfered list 116.

MAC scheduler 26 may further generate, for one of cable modems 16, sayCM₁, interfering list 118 associated with the frequency range.Interfering list 118 comprises a second list of cable modems whoseupstream transmissions in the frequency range interfere with downstreamreception of cable modem CM₁ in the frequency range. Assume, merely forexample purposes, that the second list of cable modems comprises cablemodems CM₂ . . . CM_(m). In other words, interfering list 118 for CM₁comprises CM₂, CM₃, . . . CM_(m). MAC scheduler 26 may repeat theinterfering list generating process for other cable modems 16 (e.g., CM₁. . . CM_(m)) in cable network 12. For example, interfering list 118 forCM₂ may comprise CM₁ and CM₃; interfering list 118 for CM₃ may compriseCM₂; etc. The interfering list generating process is repeated for otherfrequency ranges F(1)-F(n) in the frequency spectrum used in cablenetwork 12. Aggregator 108 may aggregate the generated interfering listsinto global interfering list 120.

In various embodiments, to generate interfered list 114 for cable modemCM₁ for a particular frequency range, say F(1), ranging scheduler 100schedules cable modem CM₁ to transmit a ranging signal within thefrequency range F(1) during a maintenance window (e.g., initial rangingwindow; contention window; etc.). Report receiver 102 receives reportsindicative of interferences on respective downstream reception at thefrequency from other cable modems CM₂ . . . CM_(m) in cable network 12.The reports include MER values. MER analyzer 104 analyzes the receivedreports and identifies cable modems CM₂ and CM₃ that are interfered bythe transmitting cable modem CM₁ based on the reports. Theidentification may be based on the value of MER exceeding apredetermined threshold (either absolute or relative). For example, CM₂and CM₃ may have reported the highest MER values among cable modems CM₂. . . CM_(m). Classifier 106 adds the identified cable modems CM₂ andCM₃ to the first list and into interfered list 114 for the cable modemCM₁.

In various embodiments, generating interfering list 118 for the cablemodem CM₁ (and other cable modems 16) comprises deriving the second listof cable modems from global interfered list 116. For example, for cablemodem CM₁ and each frequency range, from global interfered list 116,classifier 106 looks up the cable modems that interfere with the cablemodem CM₁ on that frequency range. The interfering cable modems areentered as entries for the cable modem CM₁ on that frequency range incorresponding interfering list 118. In various embodiments, interferinglist 118 and interfered list 114 are not updated often; they may beupdated when changes are made to cable network 12, for example,additional cable modems are added, or existing cable modems are removed.

Frequency planner 110 assigns respective downstream reception frequencyranges and upstream transmission frequency ranges for cable modems 16(CM₁ . . . CM_(m)) based on global interfered list 116 and globalinterfering list 120. For example, CM₁ may be assigned downstreamreception frequency range F(1) and upstream transmission frequency rangeF(3); CM₂ may be assigned downstream reception frequency range F(3) andupstream transmission frequency range F(n); and so on. In variousembodiments, the assigning is on a first-come-first serve basis. Forexample, downstream reception frequency range may be selected from amongthe frequency ranges and assigned to the first available (e.g.,recognized, identified, listed, sorted, etc.) unassigned cable modem tothe exclusion of other cable modems based on global interfered list 116and global interfering list 120.

The assigning may be based on un-aggregated lists alternatively in someembodiments. Note that the aggregation operation is merely forconvenience and may be skipped without departing from the scope of theembodiments. MAC scheduler 26 transmits to cable modems 16 (CM₁ . . .CM_(m)) corresponding assignment information comprising the respectiveassigned downstream reception frequency ranges and upstream transmissionfrequency ranges.

In some embodiments, group generator 112 groups cable modems 16 intointerference groups 30, each interference group being isolated onfrequency basis from other interference groups, with cable modems ineach group being assigned a common downstream reception frequency rangeand a common upstream transmission frequency range. For example, cablemodems CM₁, CM₂ and CM₃ may be assigned to group A. Cable modems CM₁,CM₂ and CM₃ may be assigned a common downstream reception frequencyrange of F(1) and a common upstream transmission frequency range ofF(2). In some embodiments, the grouping is based on interfered list 114.For example, the cable modem CM₁ is grouped with the first list of cablemodems comprising the cable modems CM₂ and CM₃ into interference group Afor the frequency range F(1). In other words, when grouping is based oninterfered list 114, downstream receptions of cable modems in eachinterference group for the corresponding frequency range are interferedby upstream transmissions of the cable modem in the correspondingfrequency range.

In some embodiments, grouping may take advantage of the natural networkarchitecture. For example, the cable modem CM₁ is grouped intointerference group A with other cable modems CM₃ and CM_(m) connected toa commonly coupled amplifier in cable network 12. In some embodiments,interference groups are further divided into a plurality of sub-groupswith relative isolation among the sub-groups, for example, in which eachsub-group comprises cable modems attached to a corresponding common tap(which is further down the network towards the cable modems than thecommon amplifier of the interference group). In various embodiments,cable modems in the interference group transmit upstream at a firstfrequency and receive downstream at a different frequency within thefrequency range. For example, the cable modem CM₁ transmits upstream atfrequency F₁ and receives downstream at frequency F₂ within frequencyrange F(n).

Turning to FIG. 13, FIG. 13 is a simplified block diagram showingexample details of CM grouping according to an embodiment ofcommunication system 10. In various embodiments, cable modems 16 may begrouped into various interference groups 30 to enable full duplexcommunication with little to no interference. For the sake of simplicityand ease of illustration, cable modems 16 are not shown explicitly inthe figure, but are merely represented by one (or more) taps andsplitters 22. It may be appreciated that each tap/splitter 22 may beconnected to one (or more) cable modems 16. Interference groups 30 maycomprise RF isolated groups that allow frequency re-use throughintelligent MAC scheduling.

Interference groups 30 provide a basis for T-R coordination in variousembodiments. In a general sense, the purpose of T-R coordination is toavoid interference among cable modems 16. T-R coordination is a2-dimensional resource allocation scheme that ensures that no CMs fromthe same interference group transmit simultaneously on a frequency thatis being used by other CMs to receive data, and vice versa. The twodimensions comprise frequency and time.

In various embodiments, for a specific CM, its interference group isconsidered to be a group of CMs whose downstream receptions areinterfered by the specific CM's upstream transmission. Interferencegroups could be frequency dependent. For example, in interference groupA, cable modems 16 transmit upstream at frequency F1, and receivedownstream at frequency F4, which is different from F1; in interferencegroup B, cable modems 16 transmit upstream at frequency F5, and receivedownstream at frequency F2; and so on. Cable modems 16 may belong tomultiple interference groups, one for each frequency (e.g., carrier). Insome embodiments, the interference may not be symmetric: a specific CMmay interfere with another CM, but not the other way around. In otherembodiments, the interference may be symmetric, with two CMs interferingwith each other. For simplicity, relevant cable modems 16 (eitherinterfere with or are interfered by, on any frequency) could be groupedinto a single interference group. Cable modems 16 within each group tendto interfere with each other, but there are no or little interferencesamong cable modems 16 in different groups.

CMs that are within the same interference group may interfere with eachother. That is, the upstream signal may not be sufficiently attenuatedto be subtracted out of the combined spectrum. In some embodiments, theinterference group may comprise CMs within the same tap group. Sincethere is no way of exactly knowing which CM is on which tap group, thishas to be measured and the resulting groupings may not align exactlywith a particular (e.g., single) tap group.

In an example embodiment, the frequency spectrum of cable network 12 maybe divided into multiple frequency ranges. In some embodiments, eachfrequency range aligns with a channel boundary. For each specific one ofcable modems 16 and each frequency range, MAC scheduler 26 may identifythose cable modems 16 whose upstream transmissions interfere withdownstream receptions of that specific one of cable modems 16, and thosecable modems 16 whose downstream receptions are interfered by upstreamtransmissions of that specific one of cable modems 16, if they operateon that same frequency. Based on such identification, MAC scheduler 26avoids assigning cable modems 16 to frequency ranges that may causeinterferences among them. Cable modems 16 operate with FDD and noneighboring cable modems 16 are assigned to overlapping downstream andupstream frequency ranges.

Turning to FIG. 14, FIG. 14 is a simplified block diagram showingfurther example details of CM grouping according to an embodiment ofcommunication system 10. In some embodiments, frequency planning canleverage isolations resulting from natural CM grouping in cable network12. Note that cable network topology is largely driven by street andhouse layout and may vary dramatically from one community to others. Thedevice performances (e.g., coupling, directivities, etc.) that dictateinterference among cable modems 16 also vary in a wide range. Typically,distribution cables are branched out at the output of amplifier 20(e.g., tree architecture). Taps and splitters 22 at amplifier 20 mayprovide approximately 20 dB isolation among cable modems 16 of eachbranch (e.g., division), whereas interference between downstream andupstream signals may be approximately 30 dB, permitting CMs in differentgroups to interfere only minimally, if at all. CMs covered by a singlebranch may belong to a single group in some embodiments. For example,two groups A and B of CMs that branch off after amplifier 20 may beunlikely to interfere with each other (cable modems 16 in group A willnot interfere with cable modems 16 in group B and vice versa).

Turning to FIG. 15, FIG. 15 is a simplified block diagram showingfurther example details of CM grouping according to an embodiment ofcommunication system 10. Multiple levels of CM grouping may beimplemented in cable network 12. CMs belonging to a single one ofinterference groups 30 could be further divided into multiple sub-groups31. For example, consider CM groups A and B, with CMs in group Atransmitting upstream at frequency F1 and receiving downstream atfrequency F2, and with CMs in group B transmitting upstream at frequencyF2 and receiving downstream at frequency F1. Some cable modems 16 ingroup A that are attached to tap P are assigned to sub-group X; othercable modems 16 in group B that are attached to tap Q are assigned toanother sub-group Y. The interferences among CMs belonging to differentsub-groups X and Y may be much less compared to interferences among CMswithin the same sub-group (say, X or Y, individually).

According to various embodiments, CM grouping based on frequencies thattake advantage of natural network architecture can improve isolationamong cable modems 16, and enable full duplex operation throughfrequency planning. CM load balancing among groups may be achievedthrough sub-level grouping. For example, cable modems 16 may be loadbalanced among groups A and B by looking into sub-level grouping, andmoving sub-groups cross groups. For example, sub-group Z initiallyassigned to group A may be regrouped into group B based on CM loadbalancing concerns. In some embodiments, frequency planning isautomated, with CM load balance as one of the metrics for automation.

Turning to FIG. 16, FIG. 16 is a simplified diagram illustrating exampledetails of interfered list 114 of a frequency planning scheme accordingto an embodiment of communication system 10. As such, a stochasticsimulation scheme with an abstract model for cable network 12 may beused in some embodiments to simulate the frequency planning scheme. Forexample, cable network 12 is modeled by two lists: interfering list 118and interfered list 114. Regardless of the cable topology and deviceperformance, the frequency planning depends substantially on the twolists; in other words, relevant properties of the network topology anddevices may be substantially fully captured by the two lists.

Example interfered list 114 may be generated for each cable modem andeach frequency range in cable network 12. For example, the frequencyspectrum may be divided into n frequency ranges and interfered list 114generated for each one of cable modems 16 for each of the n frequencyranges. Interfered list 114 may be sorted according to frequency rangesin some embodiments, as shown in the FIGURE. For example, for frequencyrange F1, downstream reception of cable modems CM′1_1, CM′1_2, . . .CM′1_n is interfered by upstream transmission of cable modem CM 1;downstream reception of cable modems CM′2_1, CM′2_2, . . . CM′2_n isinterfered by upstream transmission of cable modem CM 2; and so on.Similar lists may be generated for each of frequency ranges F1, F2, . .. Fn. In some embodiments, the different lists may be collapsed into asingle list, such as global interfered list 116 for example, forconvenience.

Turning to FIG. 17, FIG. 17 is a simplified flow diagram illustratingexample operations 130 for frequency planning that may be associatedwith an embodiment of communication system 10. Initially, globalinterfered list 116 and global interfering list 120 are generated. Theoperations may start at 132, at which a cable modem CM(i) is selectedwith index i initialized to 1 in the first iteration. At 134, frequencyrange F(j) is selected as the downstream reception frequency range toselected CM(i), with index j initialized to 1 in the first iteration. Inother words, the first available cable modem is tentatively assigned thefirst selected frequency range in the first iteration. At 136, cablemodems that may interfere with CM(i) is identified by looking up thecorresponding entry for CM(i) in interfering list 118 for F(j).

At 138, a determination is made whether any of the identified cablemodems have been assigned F(j) as the upstream transmission frequency.If yes, at 140, a determination is made whether the selected frequencyrange F(j) is the last block of available frequency ranges; that is,whether frequency index j is equal to the maximum value of number offrequency ranges, n. If yes, CM(i) is tagged at 142 as not supportingfull duplex communication (symmetrical is the same as full-duplexcommunication as used herein). The operations step to 144, at which adetermination is made whether the selected cable modem CM(i) is the lastavailable cable modem (in other words, whether index i is equal to themaximum value of number of cable modems, m). If not, at 145, cable modemindex i is incremented by 1, and the operations step to 132 and continuethereafter. If the selected cable modem CM(i) is the last availablecable modem, a determination is made at 146 whether the iteration is themaximum number of allowed iterations. If not, the operations continue to132 with a new frequency index permutation. Otherwise, the operationsend. Turning back to 140, if the frequency index j is not n, it isincremented by 1 at 147, and the operations step to 134 and continuethereafter. Turning back to 138, if no cable modems have been assignedF(j) as the upstream transmission frequency, at 148, F(j) is assigned asthe downstream reception frequency for CM(i).

At 150, F(j′) is selected as the upstream transmission frequency forcable modem CM(i), with j′ initialized to 1 in the first iteration. At152, cable modems are identified that may be interfered by CM(i) bylooking up the corresponding entry for CM(i) in interfered list 114 forF(j′). At 154, a determination is made whether any of the identifiedcable modems have been assigned a downstream reception frequency rangeof F(j′). If yes, at 156 a determination is made whether the selectedfrequency range F(j′) is the last block of available frequency ranges;that is, whether frequency index j′ is equal to the maximum value ofnumber of frequency ranges, n. If yes, at 158, CM(i) is tagged as notsupporting full duplex communication, and the operations step to 144 andcontinue thereafter. If the frequency index j′ is not n, it isincremented by 1 at 159, and the operations step to 150. Turning back to154, if no cable modems have been assigned F(j′) as the downstreamtransmission frequency range, at 148, F(j) is assigned as the downstreamreception frequency range for CM(i) at 160. The operations step to 144and continue thereafter.

In various embodiments, operations 130 may not be fully optimized; forexample, downstream reception and upstream transmission frequency rangesare assigned on a first-come-first-serve (FCFS) basis. As differentcable modems may have different interfere characteristics (e.g., somemay interfere with more cable modems, some less), FCFS may not result inan optimized frequency assignment (e.g., many cable modems may fail tosupport full duplex communication). To more fully exploit isolationsamong cable modems, the frequency ranges may be assigned such that cablemodems with better isolations are grouped together and assigned with thesame frequency range, leaving more frequency ranges for cable modemsthat require different frequency ranges to avoid interferences. In someembodiments, the iterations may be performed assigning each cable modemwith each of the frequency ranges F(1) . . . F(n) for both downstreamreception and upstream transmission, and the best combination offrequency ranges (e.g., one with the least number of interfered cablemodems) may be selected as the final assignment. However, to cover allthe cable modems, and all the frequencies, for both downstream receptionand upstream transmission, the total number of the iterations requiredto final assignment is (n^m)^2, where n is the number of frequencyranges, and m is the number of cable modems. With n=6, m=128, there willbe total 1.6096e¹⁹⁹ iterations, which may not be practical with existingprocessors.

In some embodiments, a sub-optimal scheme may be implemented, in whichthe frequency index is permuted, and the frequency assignments are basedon first-come-first-serve with respect to the cable modems, but with thepermuted frequency index. The frequency assignment iterations areexecuted multiple times, each time with different, randomly selectedfrequency ranges, and the best combination of downstream and upstreamfrequency ranges are selected from the completed iterations. Simulationsshow that an optimal performance can be achieved with approximately 200frequency permutations. The frequency planning (with the optimizationstep) can be tedious, but it may occur infrequently (e.g., frequencyassignment may be performed only if there are changes to the network,such as addition of new taps, cable modems, etc.). In some embodiments,the frequency assignment may be performed offline, for example, with asoftware designed networking (SDN) application.

Turning to FIG. 18, FIG. 18 is a simplified block diagram illustratingexample details of transceiver 18 according to an embodiment ofcommunication system 10. In various embodiments, each of downstream andupstream signals uses the complete frequency spectrum during full duplexcommunication. As a result, a transmitted signal 162 (comprisingdownstream data from CMTS 14 to cable modems 16) and a received signal164 (comprising upstream data from cable modems 16 to CMTS 14) overlapin frequency and time at transceiver 18. Typically, transmitted signal162 has a higher signal level (e.g., with more power) than receivedsignal 164, and can completely wipe out received signal 164 if there isnot sufficient isolation between a transmitter portion 166 and areceiver portion 168 of transceiver 18. In various embodiments, toenable full duplex communication in cable network 12, interferences fromtransmitter portion 166 may be suppressed at receiver portion 168 usingan AIC algorithm implemented in a DSP 170 in transceiver 18. DSP 170includes a memory element for storing instructions and dataappropriately. A clock module 171 facilitates timing functions for theAIC algorithm. In various embodiments, clock module 171 may be embeddedin DSP 170. DSP 170 may be configured to perform FFT/IFFT or otherstandard DSP operations. Embedded processors for control operations andI/O operations, with support for floating point operations may also beincluded in DSP 170.

Interference is a limiting factor in quality of full duplexcommunications. Different from background noise, distortion effect ofself-interference cannot be mitigated by increasing transmission powerbecause the amount of interference is directly proportional to thesignal power itself. OFDM scheme suffers from interference especiallywhen time variation exists in the channel between transmitter portion166 and receiver portion 168.

In various embodiments, interferences coupled to receiver portion 168arise from transmitter portion 166 due to full duplex communication, inwhich downstream and upstream frequencies overlap. In theory,transmitted signal 162 is known to, or can be accessed by, receiverportion 168 in transceiver 18; ideally, a copy of transmitted signal 162may be used as a reference signal to cancel out interferences atreceiver portion 168. However, the copy of transmitted signal 162received by receiver portion 168 as the reference is an “ideal”transmitted signal, without any channel effect (e.g.,micro-reflections), whereas the actual interference coupled throughreceiver portion 168 has channel effects. In various embodiments, theAIC algorithm executing in DSP 170 estimates the channel effects oftransmitted signal 162 through a channel estimation algorithm. Receiverportion 168 imposes the estimated channel effects onto the ideal copy oftransmitted signal 162, and uses the modified copy of transmitted signal162 to cancel out the interference.

Turning to FIG. 19, FIG. 19 is a simplified block diagram illustratingexample details of transceiver 18 according to an embodiment ofcommunication system 10. On a downstream pathway 172, an OFDM signalbaseband generator (not shown) generates a baseband reference signal. Inan example embodiment, the baseband reference signal comprises apseudo-random binary sequence (PRBS) signal with a bandwidth of 12.8MHz, at a clock rate of 20.48 MHzm with OFDM characteristics includingsubcarrier spacing of 20 kHz, Fast Fourier size of 1024, and a cyclicprefix up to 1.2207 μs (e.g., 25 time-domain samples). In someembodiments, an external interface with an external OFDM signalgenerator inputs data to be transmitted in the OFDM baseband referencesignal. In some embodiments, the baseband signal with data is up sampledby 20 times to 409.6 MHz, for example, to tune to any desired locationin a frequency spectrum from 0 MHz to 150 MHz. The 20 time oversamplesare split into 3 steps of 5 times, 2 times and 2 times, respectively,with half band harmonics suppression filtering. A quadrature modulatormodulates the oversampled signal to generate a digital baseband OFDMsignal 174 (for the sake of brevity, digital baseband (BB) OFDM signalmay alternatively be referred to as simply BB signal).

BB signal 174 is provided as a reference signal to an AIC module 176(e.g., implemented in DSP 170). AIC module 176 comprises a block ofinstructions implementing an appropriate AIC algorithm. BB signal 174 isfurther converted to RF signal 162 at a digital to analog converter(DAC) 177; an amplifier 178 amplifies RF signal 162. A two-waycombiner-splitter 179 transmits amplified RF signal 162 out oftransceiver 18 on downstream pathway 172.

Transmitted RF signal 162 may be reflected back to transceiver 18 on anupstream pathway 180 in one or more frequencies that overlap with thoseof signals in upstream pathway 180 due to full duplex operation.Upstream pathway 180 refers to portions of transceiver 18 that includecommunication pathway of upstream signals (to CMTS 14 from cable modems16). Thus, the reflected signal may interfere with another upstreamtransmission (e.g., from cable modems 16) on upstream pathway 180,generating RF signal 164, comprising the upstream transmissioninterfered by the reflected signal. In various embodiments, it may bedesirable to extract the upstream transmission without the interferencesfrom the reflected signal.

RF signal 164 may be received at two-way combiner-splitter 179. Aportion of received RF signal 164 may be reflected back on downstreampathway 172, interfering with RF signal 162 generating an RF referencesignal 182, which is provided to AIC module 176 as a digital signalafter conversion by an analog-to-digital converter (ADC) 183. Onupstream pathway 180, received RF signal 164 is amplified by anamplifier 184, converted to a digital signal by an ADC 185 and fed toAIC module 176.

AIC module 176 reduces interferences in RF signal 164 from the reflectedsignal based on BB reference signal 174 and RF reference signal 182,producing desired signal 186 as output. In a general sense, a channelimpulse response can be measured from BB reference signal 174 and RFreference signal 182. In various embodiments, AIC module 176 executesthe AIC algorithm and cancels out interferences in received RF signal164 from transmitted RF signal 162. In some embodiments, prior tointerference cancellation, RF signal 164 may be processed through aquadrature demodulator and subjected to decimation, at which thereceived 409.6 intermediate frequency (IF) signal is decimated by 20times to a 20.48 MHz base band signal. In some embodiments, the 20 timedecimations are split into three steps of 2 times, 2 times and 5 timesrespectively, with half band aliasing filtering. Harmonic suppressionfilters used at over sampling is reused as anti-aliasing filters.

In various embodiments, interference-canceled signal 186 is subjected todemodulation and fed to an OFDM signal receptor (not shown). OFDM signalreception after interference cancellation may include the followingfeatures: time tracking, frequency tracking (e.g., which may not be usedif transmitter portion 166 and receiver portion 168 share the samesystem clock 171), channel estimation, cyclic prefix removal, InverseFast Fourier Transform (IFFT), constellation computation and MERcomputations. In some embodiments, the OFDM signal processing portion ofreceiver portion 168 may be implemented offline in an external computingdevice. The interference-canceled signal may be sent to the externalcomputing device and post-processed with appropriate post processingalgorithms.

Turning to FIG. 20, FIG. 20 is a simplified block diagram illustratingexample details of transceiver signal flows and interferencecancellation according to an embodiment of communication system 10.Transmitted RF signal 162 on downstream pathway 172 can loop back viamultiple pathways. In general, transmitted RF signal 162 is reflectedback to transceiver 18 from cable network 12. For example, one of thereflections may be through port coupling of two-way combiner-splitter179; other reflections may occur at taps/splitters 22 from signalringing at the respective taps/splitters 22. The reflected signalcomprises time-shifted samples of transmitted RF signal 162, eachtime-shifted sample attenuated by differing amounts relative totransmitted RF signal 162.

Assume the gain of amplifier 176 is ˜30 dB, and isolation between twooutput ports of 2-way combiner-splitter 177 is ˜30 dB. The feedbacksignal through combiner port coupling may be 30 dB below the mainsignal, which, comparing to the interference resulting from the signalringing, contributes only a small portion of the total interference. Thefeedback through signal ringing could be more dominant. Assume thenominal return loss of a tap is ˜20 dB, with an additional 4 dB loss ofcable/combiner, the reflected portion of transmitted signal 162 may be 6dB above the desired signal on upstream pathway 180 of transceiver 18.For mathematical simplicity, interference from signal ringing (e.g.,reflection of transmitted signal 162 into upstream pathway 180 andreflection of received signal 164 into downstream pathway 172) may bemore dominant that reflections from outside transceiver 18.

For purposes of explaining mathematically, BB reference signal 174 isreferred to in the figure as tx1′ or alternatively as rx_r0; RFreference signal 182 comprises tx2′ (referring to transmitted signal162) and rx0 (comprising a portion of received RF signal 164) and isreferred to, for mathematical convenience, as rx_r; τ corresponds todelay, with τ_i being delay on upstream pathway 180, and τ_r being delayon downstream pathway 172. Explanations of the mathematical symbols(e.g., notations) in the figure described herein are presented in thefollowing table:

Symbol Relationship Note Channel rx0 received signal received signal onupstream pathway ideal BB signal, HFC channel rx_i rx_i = tx2′ receivedinterference on upstream 2:1 combiner + HFC pathway (approximated to besame as channel transmitted RF signal merely for simplicity ofexplanation) rx rx = rx0 + c1*rx_i total received signal on upstreampathway; c1 is scaling factor rx_r rx_r = tx2′ + c2*rx0 RF referencesignal; c2 is scaling factor hardware channel (reflection of receivedsignal on downstream pathway approximated to be a scaled factor ofreceived signal merely for simplicity of explanation) rx_r0 rx_r0 = tx1′BB reference signal no additional channel tx0 tx0 = conv(w1, rx) −received signal on upstream pathway after no additional channel conv(w0,rx_r) interference cancellation; conv refers to convolution function; w0and w1 are convolution coefficients tx1′ transmitted BB signal ondownstream no additional channel pathway tx2′ Fcn(tx1′) transmitted RFsignal on downstream nonlinear channel, pathway; Fcn refers to noise,amplification noise and DAC functions

AIC module 176 performs numerous iterations according to the AICalgorithm to reduce interference. In some embodiments, the AIC algorithmcomprises calculating values of scaling factors c1 and c2, andconvolution coefficients w1, w0, which are used to compute and cancelinterferences of the transmitted and received signals. AIC module 176performs interference calculations using various mathematical functions,including convolution. In a general sense, convolution is a mathematicaloperation on two functions, producing a third function that is typicallyviewed as a modified version of one of the original functions. Forexample, convolution is the integral of the product of the two functionsafter one is reversed and shifted. Mathematically, convolution offunctions f(t) and g(t) can be written as (f*g)(t) to be:(ƒ*g)(t)=∫₀ ^(∞)ƒ(t−τ)g(τ)dτConvolution is applicable because interferences can appear due totime-shifting or time lag between transmitted signals and reflectedsignals (e.g., signal at time t interfered by reflection of transmittedsignal at time t−τ; and so on). In a general sense, convolution in thetime domain can be represented by multiplication in the frequencydomain. The AIC algorithm performs convolutions on received RF signal164 and RF reference signal 182, followed by a cancellation of theconvoluted RF reference signal from the convoluted received RF signal.The AIC algorithm uses convolution coefficients w0 and w1 ontime-shifted samples of received RF signal 164 and RF reference signal182 that account for time delays in reflection, the time-shifted samplesbeing weighted with scaling factors c1 and c2 (e.g., to account forattenuations). The AIC algorithm iteratively calculates convolutioncoefficients w0 and w1 and scaling factors c1 and c2.

Turning to FIG. 21, FIG. 21 is a simplified block diagram illustratingexample details of AIC module 176 according to an embodiment ofcommunication system 10. AIC module 176 includes a FFT module 190 forseparating incoming signals (e.g., RF signals 164 and 182) into aplurality of subcarriers (e.g., M subcarriers). A plurality of AICblocks 192 (e.g., AIC₀, AIC₁, . . . . AIC_(M−1)) corresponding to theplurality of subcarriers perform AIC iterations on the respectivesignals. RF reference signal 182 is provided to FFT module 190 afterconverting to a digital signal (e.g., by ADC 183 ); likewise received RFsignal 164 is input to FFT module 190 after converting to a digitalsignal (e.g., by ADC 185). Because full duplex communication implies acommon frequency range for upstream and downstream, BB reference signal174 and RF reference signal 182 can indicate the common channel impulseresponse for both upstream and downstream communication. The transformedsignals from FFT module 190 may be separated out into individualsubcarrier frequencies based on information of the plurality ofsubcarrier frequencies comprised in digital reference signal 174. EachAIC block 192 may separately execute the AIC algorithm to reduceinterferences.

Turning to FIG. 22, FIG. 22 is a simplified block diagram illustratingexample details of AIC module 176 according to an embodiment ofcommunication system 10. R(t) is RF reference signal 182 input into AICmodule 176; I(t) is the interference signal coupled with desired signal186; Z(t) is input RF signal 164, and comprises a combination ofinterference signal I(t) and desired signal S(t). AIC algorithms mayexecute assuming interference from signals during a time intervaldivided into n periods. For example, the interference may comprisereference signal R(t), R(t−τ), R(t−2τ) . . . R(t−(n−1)τ). Eachtime-shifted sample R(t−τ), R(t−2τ) . . . R(t−(n−1)τ) may be attenuatedsuitably. The attenuation may be captured as weighting factors c₀, c₁, .. . c_(N−1), corresponding to the n periods. For example, estimatedinterference signal based on the reference signal comprisesc₀R(t)+c₁R(t−τ)+ . . . +c_(N−1)R(t−(n−1)τ). In an example embodiment,the weighting factors may comprise a combination of scaling factors c1and c2 and convolution coefficients w0 and w1.

The estimated interference signal may be compared with the input signaland a residue, comprising the difference, computed. The residue may beused to update values of weighting factors c₀, c₁, . . . c_(N−1)suitably. The residue can indicate that further iterations are in order,and values of weighting factors c₀, c₁, . . . c_(N−1) may be updated andthe operations repeated until an acceptable residue is obtained. The AICalgorithm can converge and take full effect within seconds. The channelsin cable network 12 being quasi-static (i.e., no mobility), the AICalgorithm can maintain tracking of channel variations caused by variousparameters such as temperature variations, environment changes, ordevice aging.

Note that in some embodiments, AIC module 176 executes the AIC algorithmas described herein separately for each subcarrier frequency. In suchembodiments, R(t), Z(t), I(t) and S(t) correspond to the portion of therespective signals (e.g., RF reference signal 182, RF signal 164,interference signal, and desired signal 186 ) corresponding to theparticular subcarrier frequency at which the AIC algorithm is beingexecuted. For example, if AIC algorithm at subcarrier frequency i isbeing executed, R_(i)(t), Z_(i)(t), I_(i)(t) and S_(i)(t) correspond toportions of RF reference signal 182, RF signal 164, interference signal,and desired signal 186 at subcarrier frequency i.

Turning to FIGS. 23A and 23B, FIGS. 23A and 23B are simplified blockdiagrams illustrating an example amplifier 20 according to an embodimentof communication system 10. Note that amplifier 20 is more complicatedthan transceiver 18, but the basic DSP building function blocks aresimilar. Amplifier 20 includes a ringing suppressor 200 each ondownstream pathway 172 and upstream pathway 180; a downstream amplifier202; an upstream amplifier 204; and a two-way combiner-splitter 206 oneach end. The DSP algorithm in ringing suppressor 200 is similar to AICmodule 176 of transceiver 18, with some modifications for echocancellation. In a general sense, discontinuities (e.g., limited returnloss of tap/splitter, etc.) are inevitably present in cable network 12,and cause signal bouncing, resulting in signal ringing. Signal ringingcan be the main source of the interferences between downstream pathway172 and upstream pathway 180 in full duplex operation.

Signal flows on downstream pathway 172 enter amplifier 20 throughtwo-way combiner-splitter 206 on one end, flows through ringingsuppressor 200 on downstream pathway 172, is amplified at downstreamamplifier 202, and exits out through two-way combiner-splitter 206 onthe other end. Signal flows on upstream pathway 180 enter amplifier 20through two-way combiner-splitter 206 on one end, flows through ringingsuppressor 200 on upstream pathway 180, is amplified at upstreamamplifier 204, and exits out through two-way combiner-splitter 206 onthe other end. The signal flows on downstream pathway 172 and upstreampathway 180 can be considered to be mirror images of each other; assuch, ringing suppressor 200 on downstream pathway 172 can be identicalwith ringing suppressor 200 on upstream pathway 180.

In some embodiments, two steps of echo cancellations are implemented inringing suppressor 200. At step 1, the AIC algorithm of transceiver 18is implemented with a relaxed cancellation specification (e.g.,suppressing interferences to a few dB below the desired signal). Some ofthe interference residue out of this step may loop back to the otherpathway of amplifier 20 where it is suppressed in step 2, and some ofthe interference residue may proceed to transceiver 18 where it iscancelled at AIC module 176 of transceiver 18. In step 2, echoes fromthe same pathway may be cancelled. The echo cancellation algorithm atstep 2 comprises a modified AIC algorithm with the reference signalbeing the output signal of the previous step on the same pathway. Toenable the echo cancellation, a delay may be added on each pathway toensure that the reflections are distinct in time from the main signal sothey can be suppressed with the echo cancellation algorithm.

To explain further, ringing suppressor 200 includes two echocancellation modules 208 and 210. Input to echo cancellation module 208includes BB reference signal 212 and RF reference signal 214 from theother pathway (e.g., for ringing suppressor 200 on upstream pathway 180,BB reference signal 212 and RF reference signal 214 are from downstreampathway 172; and vice versa). Unlike transceiver 18, amplifier 20requires echo cancellation on each pathway from its own signal. To thisend, echo cancellation module 210 performs echo cancellation on signalsoutput from echo cancellation module 208. The reference signal to echocancellation module 210 may comprise a time-shifted output signal fromecho cancellation module 208. In an example embodiment, the timeshifting may be by two time periods (2τ). The digital portion of theoutput from echo cancellation module 210 may be fed as BB referencesignal 212 to ringing suppressor 200 on the other pathway.

Turning to FIG. 23B, FIG. 23B shows example mathematical details ofamplifier 20 according to an embodiment of communication system 10.Amplifier 20 can be considered to comprise mirror images 216 and 218around imaginary separator 219. Each portion 216 and 218 comprises anamplifier, a signal flowing through downstream pathway 172, anothersignal flowing through upstream pathway 180, and two echo cancellationmodules 208 and 210. For the sake of simplicity, echo cancellationmodule 208 is referred to as equalizer 1 (EQ1), and echo cancellationmodule 210 is referred to as equalizer 2 (EQ2). EQ1 computes convolutioncoefficients w0, and w1; EQ2 computes convolution coefficient w2. Thevarious symbols and notations in the figure are explained in thefollowing table:

Signals Relationship Note Channel rx0 received signal received signal onupstream pathway ideal BB signal, HFC channel rx_i rx_i = tx2′ receivedinterferences on upstream 2:1 combiner + HFC pathway channel rx rx =rx0 + c1*rx_i total received signal on upstream pathway; c1 is a scalingfactor rx_r rx_r = tx2′ + c2*rx0′ received RF reference signal onhardware channel upstream pathway; c2 is a scaling factor rx_r0 rx_r0 =tx1′ received BB reference signal on no additional channel upstreampathway tx0 tx0 = conv(w1, rx(t − τ_i) − transmitted signal after firstno additional channel conv(w0, rx_r(t − τ_r)) interference cancellationon upstream pathway; 1 ≦ τ ≦ min(τ_i, τ_r), τ corresponding to delay,with τ_i being the delay on the upstream pathway, and τ_r being thedelay on the downstream pathway tx1 tx1 = tx0 − conv(w2, tx0(t −transmitted signal after second no additional channel 2τ_i))interference cancellation on upstream pathway tx2 Fcn(tx1) transmittedRF signal on upstream nonlinear channel, pathway; Fcn refers to noise,noise amplification and DAC functions rx0′ received signal receivedsignal on downstream ideal BB signal, HFC pathway channel rx_i′ rx_i′ =tx2 received interferences on downstream 2:1 combiner + HFC pathwaychannel rx′ rx′ = rx0′ + c1′*rx_i′ total received signal on downstreamhardware channel pathway; c1′ is a scaling factor rx_r′ rx_r′ = tx2 +c2′*rx0 received RF reference signal on hardware channel downstreampathway; c2′ is a scaling factor rx_r0′ rx_r0′ = tx1 received BBreference signal on no additional channel downstream pathway tx0′ tx0′ =conv(w1′, rx′(t − τ_i) − transmitted signal after first no additionalchannel conv(w0′, rx_r′(t − τ_r)) interference cancellation ondownstream pathway tx1′ tx1′ = tx0′ − conv(w2′, transmitted signal aftersecond no additional channel tx0′(t − 2τ_i)) interference cancellationon downstream pathway tx2′ Fcn(tx1′) transmitted RF signal on downstreamnonlinear channel, pathway; Fcn refers to noise, noise amplification andDAC functions Each pathway generates 4 signals (e.g., rx, tx0, tx1, andtx2 on upstream pathway and rx′, t0′, tx1′ and tx2′ on downstreampathway), and receives three signals, rx_i, rx_r, rx_r0, from the otherpathway. c1, c2, c1′, and c2′ are constants (scaling factors)

Turning to FIG. 24, FIG. 24 is a simplified diagram showing an exampleAIC algorithm 220 for computing convolution coefficients according to anexample embodiment. Equalizer 208 (EQ1) of amplifier 20, and AIC module176 of transceiver 18 execute algorithm 220 and determines values ofconvolution coefficients w0 and w1. AIC algorithm 220 presented hereinis in MATLAB language. However, it will be appreciated by persons withskill in the art that any suitable programming language may be used toimplement AIC algorithm 220 within the broad scope of the embodiments.

Turning to FIG. 25, FIG. 25 is a simplified diagram showing an exampleecho cancellation algorithm 222 for computing convolution coefficientsaccording to an example embodiment. Equalizer 210 (EQ2 or EQ2′) ofamplifier 20 executes echo cancellation algorithm 222 and determinesvalues of convolution coefficient w2. Echo cancellation algorithm 222presented herein is in MATLAB language. However, it will be appreciatedby persons with skill in the art that any suitable programming languagemay be used to implement echo cancellation algorithm 222 within thebroad scope of the embodiments.

Turning to FIG. 26, FIG. 26 is a simplified block diagram illustratingexample details of a hardware implementation of amplifier 20 accordingto an embodiment of communication system 10. Amplifier 20 may includedownstream amplifier 202, upstream amplifier 204, a downstream receivemodule 224 and an upstream receive module 226. Each receive module 224may be similar to receiver portion 168 of transceiver 18. A DSP 228 mayexecute AIC algorithm 220 and echo cancellation algorithm 222. In someembodiments, ringing suppressor 200 may be implemented in DSP 228. Aclock 230 may facilitate timing operations of DSP 228. Various modules,such as downstream amplifier 202, upstream amplifier 204, downstreamreceive module 224 and upstream receive module 226 may be RF shieldedfrom each other appropriately.

Turning to FIG. 27, FIG. 27 is a simplified flow diagram illustratingexample operations 250 associated with interference cancellationaccording to an embodiment of communication system 10. At 252, a BBreference signal (e.g., tx1′) is generated on a first pathway (e.g.,downstream pathway 172 or upstream pathway 180) of a network element. Asused herein, the term “network element” encompasses a transceiver (e.g.,transceiver 18), an amplifier (e.g., amplifier 20), or other networkcomponent of cable network 12 supports full duplex communication, andthrough which signals flow in an upstream direction and downstreamdirection in overlapping frequency ranges. If the network element is atransceiver, the BB reference signal tx1′ may be generated attransceiver 14; if the network element is an amplifier, the BB referencesignal may be provided from a second pathway (e.g., if the first pathwayis downstream pathway 172, the second pathway is upstream pathway 180,and vice versa).

At 254, the BB reference signal tx1′ is converted to a first RF signaltx2′. At 256, the BB reference signal tx1′ is provided to a signalprocessor (e.g., DSP 170, DSP 228) as BB reference signal rx_r0. At 258,the first RF signal tx2′ is transmitted on the first pathway. At 260,the first RF signal tx2′ is reflected into the second pathway. At 262,the reflection (e.g., rx_i) interferes with signals (e.g., rx0) on thesecond pathway generating a second RF signal rx (rx=rx0+c1*rx_i) on thesecond pathway. At 264, the second RF signal rx is provided as input tothe signal processor (e.g., after suitably amplifying and converting todigital domain). At 266, the second RF signal is reflected into thefirst pathway. At 268, the reflection interferes with first RF signaltx2′ generating RF reference signal rx_r on the first pathway(rx_r=tx2′+c2*rx0). At 270, the RF reference signal rx_r is provided tothe signal processor (e.g., after suitably amplifying and converting todigital domain). At 272, the signal processor reduces interferences inthe second RF signal rx from reflections of the first RF signal tx2′based on the BB reference signal rx_r0 and RF reference signal rx_r togenerate output tx0. At 274, if the network element is an amplifier(e.g., as opposed to a transceiver), the signal processor furtherreduces interferences in the second RF signal rx from echoes of itselfto generate output tx1; in effect a time-shifted sample of tx0 is fed asthe reference signal for echo cancellation purposes. In someembodiments, the time-shifting is equal to two time periods (e.g., 2τ)at 276. Operations 252 to 276 described so far comprise interferencecancellations on the second pathway due to reflections from the firstpathway.

At 278, the first branch and the second branch are transposedfiguratively. In other words, the output tx1 comprises the BB signal onthe second pathway, which is fed into the AIC module of the firstpathway as the BB reference signal for interference cancellation on thefirst pathway. Operations 252 to 276 are repeated for interferencecancellations on the first pathway due to reflections from the secondpathway. Note that the transceiver does not have parallel mirror-imagepathways and is less complex than the amplifier in regards tointerference cancellation operations.

Turning to FIG. 28, FIG. 28 is a simplified flow diagram illustratingexample operations 280 that may be associated with AIC operationsaccording to an example embodiment of communication system 10. At 282,the input signal (rx, rx′) and the reference signal (e.g., rx_r, rx_r′)provided to the signal processor (e.g., DSP 170, DSP 228 ) may beseparated into subcarrier frequencies in the digital domain (e.g., afterFFT, and comparison with BB reference signal rx_r0, rx_r0′). The inputsignal refers to the signal to be processed to remove interferences. At284, the input signal is subjected to a convolution function. Forexample, the convolution function may result in a signal comprisingweighted time-shifted samples of the input signal. At 286, the referencesignal is subjected to another convolution function. For example, theanother convolution function may result in another signal comprisingweighted time-shifted samples of the reference signal. At 290, theconvoluted reference signal is cancelled (e.g., subtracted) from theconvoluted input signal. Operations 284-290 may be repeated at eachsubcarrier frequency.

Turning to FIG. 29, FIG. 29 is a simplified flow diagram illustratingexample operations 300 that may be associated with AIC operationsaccording to an example embodiment of communication system 10. At 302,time-shifted samples of RF reference signal (R(t)) is determined (e.g.,at time t, t−τ, t−2τ, . . . t−(n−1)τ). At 304, weighting factors (e.g.,C₁, C₂, . . . C_(N−1)) is estimated. At 306, an interference signal isestimated as a weighted sum of the time-shifted samples (e.g., Σ₀ ^(n−1)R(t−iτ)). At 308, a residue is calculated between the estimatedinterference signal and the input signal (Z(t)). At 310, a determinationis made whether the calculated residue is less than a predeterminedthreshold. If not, at 312, the weighting factors are updated based onthe calculated residue and the operations loop back to 306, and continuethereafter in successive iterations. If the residue is less than thepredetermined threshold, at 314, the output signal (S(t)) is determinedto be the input signal without interferences (e.g., S(t)=Z(t)−I(t)).

Turning to FIGS. 30A, 30B, and 30C, FIGS. 30A, 30B, and 30C showsimulation results with various amplifier types. FIG. 30A shows receivedsignal constellations with amplifier 20 that does not include echocancellation module 210 (e.g., without EQ2). At receiver input, theinterference level is 14 dBM, and desired signal level is 0 dBm. The SNRof desired signal (thermal noise, without impairments) is 50 dB. FIG.30B shows signal quality of signal tx2, and FIG. 30C shows signalquality of signal tx2′.

Note that in this Specification, references to various features (e.g.,elements, structures, modules, components, steps, operations,characteristics, etc.) included in “one embodiment”, “exampleembodiment”, “an embodiment”, “another embodiment”, “some embodiments”,“various embodiments”, “other embodiments”, “alternative embodiment”,and the like are intended to mean that any such features are included inone or more embodiments of the present disclosure, but may or may notnecessarily be combined in the same embodiments. Furthermore, the words“optimize,” “optimization,” and related terms are terms of art thatrefer to improvements in speed and/or efficiency of a specified outcomeand do not purport to indicate that a process for achieving thespecified outcome has achieved, or is capable of achieving, an “optimal”or perfectly speedy/perfectly efficient state.

In example implementations, at least some portions of the activitiesoutlined herein may be implemented in software in, for example, CMTS 14,MAC scheduler 26, amplifier 20, and transceiver 18. In some embodiments,one or more of these features may be implemented in hardware, providedexternal to these elements, or consolidated in any appropriate manner toachieve the intended functionality. The various components may includesoftware (or reciprocating software) that can coordinate in order toachieve the operations as outlined herein. In still other embodiments,these elements may include any suitable algorithms, hardware, software,components, modules, interfaces, or objects that facilitate theoperations thereof.

Furthermore, CMTS 14, MAC scheduler 26, amplifier 20, and transceiver 18described and shown herein (and/or their associated structures) may alsoinclude suitable interfaces for receiving, transmitting, and/orotherwise communicating data or information in a network environment.Additionally, some of the processors and memory elements associated withthe various nodes may be removed, or otherwise consolidated such that asingle processor and a single memory element are responsible for certainactivities. In a general sense, the arrangements depicted in the FIGURESmay be more logical in their representations, whereas a physicalarchitecture may include various permutations, combinations, and/orhybrids of these elements. It is imperative to note that countlesspossible design configurations can be used to achieve the operationalobjectives outlined here. Accordingly, the associated infrastructure hasa myriad of substitute arrangements, design choices, devicepossibilities, hardware configurations, software implementations,equipment options, etc.

In some of example embodiments, one or more memory elements (e.g.,memory element 28) can store data used for the operations describedherein. This includes the memory element being able to storeinstructions (e.g., software, logic, code, etc.) in non-transitorymedia, such that the instructions are executed to carry out theactivities described in this Specification. A processor can execute anytype of instructions associated with the data to achieve the operationsdetailed herein in this Specification. In one example, processors (e.g.,processor 27, DSP 170, DSP 228) could transform an element or an article(e.g., data) from one state or thing to another state or thing. Inanother example, the activities outlined herein may be implemented withfixed logic or programmable logic (e.g., software/computer instructionsexecuted by a processor) and the elements identified herein could besome type of a programmable processor, programmable digital logic (e.g.,a field programmable gate array (FPGA), an erasable programmable readonly memory (EPROM), an electrically erasable programmable read onlymemory (EEPROM)), an ASIC that includes digital logic, software, code,electronic instructions, flash memory, optical disks, CD-ROMs, DVD ROMs,magnetic or optical cards, other types of machine-readable mediumssuitable for storing electronic instructions, or any suitablecombination thereof.

These devices may further keep information in any suitable type ofnon-transitory storage medium (e.g., random access memory (RAM), readonly memory (ROM), field programmable gate array (FPGA), erasableprogrammable read only memory (EPROM), electrically erasableprogrammable ROM (EEPROM), etc.), software, hardware, or in any othersuitable component, device, element, or object where appropriate andbased on particular needs. The information being tracked, sent,received, or stored in communication system 10 could be provided in anydatabase, register, table, cache, queue, control list, or storagestructure, based on particular needs and implementations, all of whichcould be referenced in any suitable timeframe. Any of the memory itemsdiscussed herein should be construed as being encompassed within thebroad term ‘memory element.’ Similarly, any of the potential processingelements, modules, and machines described in this Specification shouldbe construed as being encompassed within the broad term ‘processor.’

It is also important to note that the operations and steps describedwith reference to the preceding FIGURES illustrate only some of thepossible scenarios that may be executed by, or within, the system. Someof these operations may be deleted or removed where appropriate, orthese steps may be modified or changed considerably without departingfrom the scope of the discussed concepts. In addition, the timing ofthese operations may be altered considerably and still achieve theresults taught in this disclosure. The preceding operational flows havebeen offered for purposes of example and discussion. Substantialflexibility is provided by the system in that any suitable arrangements,chronologies, configurations, and timing mechanisms may be providedwithout departing from the teachings of the discussed concepts.

Although the present disclosure has been described in detail withreference to particular arrangements and configurations, these exampleconfigurations and arrangements may be changed significantly withoutdeparting from the scope of the present disclosure. For example,although the present disclosure has been described with reference toparticular communication exchanges involving certain network access andprotocols, communication system 10 may be applicable to other exchangesor routing protocols. Moreover, although communication system 10 hasbeen illustrated with reference to particular elements and operationsthat facilitate the communication process, these elements, andoperations may be replaced by any suitable architecture or process thatachieves the intended functionality of communication system 10.

Numerous other changes, substitutions, variations, alterations, andmodifications may be ascertained to one skilled in the art and it isintended that the present disclosure encompass all such changes,substitutions, variations, alterations, and modifications as fallingwithin the scope of the appended claims. In order to assist the UnitedStates Patent and Trademark Office (USPTO) and, additionally, anyreaders of any patent issued on this application in interpreting theclaims appended hereto, Applicant wishes to note that the Applicant: (a)does not intend any of the appended claims to invoke paragraph six (6)of 35 U.S.C. section 112 as it exists on the date of the filing hereofunless the words “means for” or “step for” are specifically used in theparticular claims; and (b) does not intend, by any statement in thespecification, to limit this disclosure in any way that is not otherwisereflected in the appended claims.

What is claimed is:
 1. A method comprising: generating a globalinterfered list for a plurality of cable modems in a cable network, theglobal interfered list comprising an aggregation of a plurality ofinterfered lists corresponding to a plurality of frequency ranges, eachinterfered list comprising cable modems whose downstream receptions areinterfered by upstream transmissions of other cable modems in thecorresponding frequency range; generating a global interfering list forthe plurality of cable modems, the global interfering list comprising anaggregation of a plurality of interfering lists corresponding to theplurality of frequency ranges, each interfering list comprising cablemodems whose upstream transmissions interfere with downstream receptionsof other cable modems in the corresponding frequency range; assigningrespective downstream reception frequency ranges and upstreamtransmission frequency ranges for the plurality of cable modems based onthe global interfered list and the global interfering list; andtransmitting to the cable modems corresponding assignment informationcomprising the respective assigned downstream reception frequency rangesand upstream transmission frequency ranges.
 2. The method of claim 1,wherein generating the global interfered list comprises: generating, fora particular cable modem in the cable network, a respective interferedlist associated with a particular one of the plurality of frequencyranges, the respective interfered list comprising a first list of cablemodems whose downstream reception in the frequency range is interferedby upstream transmissions of the particular cable modem in the frequencyrange; repeating generating the interfered list for other cable modemsin the plurality of cable modems and for other frequency ranges in theplurality of frequency ranges; and aggregating the generated interferedlists into the global interfered list.
 3. The method of claim 2, whereingenerating the respective interfered list for the particular cable modemcomprises: during a maintenance window, scheduling the particular cablemodem to transmit a ranging signal within the particular one of theplurality of frequency ranges; receiving reports indicative ofinterferences on respective downstream reception in the particular oneof the plurality of frequency ranges from other cable modems in thecable network; identifying cable modems that are interfered by thetransmitting cable modem based on the reports; and adding the identifiedcable modems to the first list.
 4. The method of claim 2, wherein theparticular cable modem is grouped with the first list of cable modemsinto an interference group for the frequency range.
 5. The method ofclaim 2, wherein the particular cable modem is grouped into a pluralityof interference groups corresponding to the plurality of frequencyranges, wherein downstream receptions of cable modems in eachinterference group for the corresponding frequency range are interferedby upstream transmissions of the cable modem in the correspondingfrequency range.
 6. The method of claim 1, wherein generating the globalinterfering list comprises: generating, for a particular cable modem inthe cable network, a respective interfering list associated with aparticular one of the plurality of frequency ranges, the respectiveinterfering list comprising a second list of cable modems whose upstreamtransmissions in the frequency range interfere with downstream receptionof the particular cable modem in the frequency range; repeatinggenerating the interfering list for other cable modems in the pluralityof cable modems and for other frequency ranges in the plurality offrequency ranges; and aggregating the generated interfering lists intothe global interfering list.
 7. The method of claim 6, whereingenerating the respective interfering list for the particular cablemodem comprises deriving the second list of cable modems from the globalinterfered list.
 8. The method of claim 1, wherein assigning respectivedownstream reception frequency ranges and upstream transmissionfrequency ranges comprises grouping cable modems into groups, each groupbeing isolated on frequency basis from other groups, wherein cablemodems in each group are assigned a common downstream receptionfrequency range and a common upstream transmission frequency range. 9.The method of claim 1, wherein the cable modems are grouped intointerference groups with other cable modems connected to a commonlycoupled amplifier in the cable network.
 10. The method of claim 9,wherein the interference group is further divided into a plurality ofsub-groups with relative isolation among the sub-groups, wherein eachsub-group comprises cable modems attached to a corresponding common tap.11. The method of claim 9, wherein cable modems in the interferencegroup transmit upstream at a first frequency and receive downstream at adifferent frequency within the frequency range.
 12. Non-transitorytangible computer-readable media that includes instructions forexecution, which when executed by a processor, is operable to performoperations comprising: generating a global interfered list for aplurality of cable modems in a cable network, the global interfered listcomprising an aggregation of a plurality of interfered listscorresponding to a plurality of frequency ranges, each interfered listcomprising cable modems whose downstream receptions are interfered byupstream transmissions of other cable modems in the correspondingfrequency range; generating a global interfering list for the pluralityof cable modems, the global interfering list comprising an aggregationof a plurality of interfering lists corresponding to the plurality offrequency ranges, each interfering list comprising cable modems whoseupstream transmissions interfere with downstream receptions of othercable modems in the corresponding frequency range; assigning respectivedownstream reception frequency ranges and upstream transmissionfrequency ranges for the plurality of cable modems based on the globalinterfered list and the global interfering list; and transmitting to thecable modems corresponding assignment information comprising therespective assigned downstream reception frequency ranges and upstreamtransmission frequency ranges.
 13. The media of claim 12, whereingenerating the global interfered list comprises: generating, for aparticular cable modem in the cable network, a respective interferedlist associated with a particular one of the plurality of frequencyranges, the respective interfered list comprising a first list of cablemodems whose downstream reception in the frequency range is interferedby upstream transmissions of the particular cable modem in the frequencyrange; repeating generating the interfered list for other cable modemsin the plurality of cable modems and for other frequency ranges in theplurality of frequency ranges; and aggregating the generated interferedlists into the global interfered list.
 14. The media of claim 13,wherein generating the respective interfered list for the particularcable modem comprises: during a maintenance window, scheduling theparticular cable modem to transmit a ranging signal within theparticular one of the plurality of frequency ranges; receiving reportsindicative of interferences on respective downstream reception in theparticular one of the plurality of frequency ranges from other cablemodems in the cable network; identifying cable modems that areinterfered by the transmitting cable modem based on the reports; andadding the identified cable modems to the first list.
 15. The media ofclaim 12, wherein generating the global interfering list comprises:generating, for a particular cable modem in the cable network, arespective interfering list associated with a particular one of theplurality of frequency ranges, the respective interfering listcomprising a second list of cable modems whose upstream transmissions inthe frequency range interfere with downstream reception of theparticular cable modem in the frequency range; repeating generating theinterfering list for other cable modems in the plurality of cable modemsand for other frequency ranges in the plurality of frequency ranges; andaggregating the generated interfering lists into the global interferinglist.
 16. The media of claim 12, wherein assigning respective downstreamreception frequency ranges and upstream transmission frequency rangescomprises grouping cable modems into groups, each group being isolatedon frequency basis from other groups, wherein cable modems in each groupare assigned a common downstream reception frequency range and a commonupstream transmission frequency range.
 17. An apparatus, comprising: amemory for storing data; and a processor operable to executeinstructions associated with the data, wherein the processor and thememory cooperate, such that the apparatus is configured for: generatinga global interfered list for a plurality of cable modems in a cablenetwork, the global interfered list comprising an aggregation of aplurality of interfered lists corresponding to a plurality of frequencyranges, each interfered list comprising cable modems whose downstreamreceptions are interfered by upstream transmissions of other cablemodems in the corresponding frequency range; generating a globalinterfering list for the plurality of cable modems, the globalinterfering list comprising an aggregation of a plurality of interferinglists corresponding to the plurality of frequency ranges, eachinterfering list comprising cable modems whose upstream transmissionsinterfere with downstream receptions of other cable modems in thecorresponding frequency range; assigning respective downstream receptionfrequency ranges and upstream transmission frequency ranges for theplurality of cable modems based on the global interfered list and theglobal interfering list; and transmitting to the cable modemscorresponding assignment information comprising the respective assigneddownstream reception frequency ranges and upstream transmissionfrequency ranges.
 18. The apparatus of claim 17, wherein assigningrespective downstream reception frequency ranges and upstreamtransmission frequency ranges comprises grouping cable modems intogroups, each group being isolated on frequency basis from other groups,wherein cable modems in each group are assigned a common downstreamreception frequency range and a common upstream transmission frequencyrange.
 19. The apparatus of claim 17, wherein generating the globalinterfered list comprises: generating, for a particular cable modem inthe cable network, a respective interfered list associated with aparticular one of the plurality of frequency ranges, the respectiveinterfered list comprising a first list of cable modems whose downstreamreception in the frequency range is interfered by upstream transmissionsof the particular cable modem in the frequency range; repeatinggenerating the interfered list for other cable modems in the pluralityof cable modems and for other frequency ranges in the plurality offrequency ranges; and aggregating the generated interfered lists intothe global interfered list.
 20. The apparatus of claim 19, whereingenerating the respective interfered list for the particular cable modemcomprises: during a maintenance window, scheduling the particular cablemodem to transmit a ranging signal within the particular one of theplurality of frequency ranges; receiving reports indicative ofinterferences on respective downstream reception in the particular oneof the plurality of frequency ranges from other cable modems in thecable network; identifying cable modems that are interfered by thetransmitting cable modem based on the reports; and adding the identifiedcable modems to the first list.